Nuke it.

[Calthropstu]

The big bad is in a gigantic fortress deep on the inside of a mountain. His engines of war are fueled by geothermal energies. Anyone trying to go in would be suicide. The entire fortress is covered in anti teleportation, ant scrying and butressed by permanent walls of force. There's an entrance but it is so well defended it'd be suicide.

The solution? Bring the entire mountain down.

How would you go about this?

[Rebel7284]

With walls of force in the picture, planar bind a ton of creatures with Disintegrate as a spell like ability?

Sphere of Ultimate Destruction is also nice.

Persisted Undermaster might be nice too.

Edit: Erupt + caster level boosts might be the most efficient single-spell, assuming the walls of force are gone.

[Maat Mons]

If it's covered in anti-divination, how do you know the Big Bad is actually there?

If people are going in and out, capture some. Read their minds to know more about the inside of the fortress. Plant mind-control effects in their brains that force them to sabotage the defenses.

Since he's reliant on geothermal energy, you can defeat him by freezing the world's core.

Have you considered building a new, better world elsewhere?

[Calthropstu]

If it's covered in anti-divination, how do you know the Big Bad is actually there?

If people are going in and out, capture some. Read their minds to know more about the inside of the fortress. Plant mind-control effects in their brains that force them to sabotage the defenses.

Since he's reliant on geothermal energy, you can defeat him by freezing the world's core.

Have you considered building a new, better world elsewhere?

Only this forum would respond to a bbeg with becoming a bigger badder bbeg.

[Kol Korran]

Some clarifications needed:
- Is this for a specific game? If so- what are the game specifics? Any more info on the opposition? On the party? (Classes, level, other resources)
- If it isnt for a specific game, still some specifications- For a published campaign setting? Level of magic in the world? Resources the party can attain? Still, more about the enemy and it's capabilities?
- Available resources in terms of source books and mags?

I know the question is about blowing it all up, but it is worthy to note that on the whole- just because an entrance is well defended, it doesn't mean you can't enter by subterfuge and deception. Is the inside defended just as well? Can the party get inside close to the bbeg using disguise and bluff/ illusion and enchantment spells, by which they may bypass most opposition? (If someone is getting out, they can be caught, interrogated, threatened/ blackmailed, impersonated and more).

[One Step Two]

Only this forum would respond to a bbeg with becoming a bigger badder bbeg.

"Professionals have standards!" - Sniper.

Okay, outside of freezing the core of the World, I'd make use of Widened Earthquake to undermine the structures around the walls of course, essentially creating sink holes. Other good options would be Elemental Swarm or Summon Elemental monolith for Earth and Magma Elementals, and use their abilities to move through earth to change the internal Magma Channels so that they channel through said Force walls, turning the area into a deathtrap.

[The Viscount]

Is it specifically anti-scrying and not general anti-divination?
If so, there is the locate city bomb, though that may not play well at every table.

[Anthrowhale]

Here's a nuke (https://forums.giantitp.com/showthread.php?621105-The-best-nuke). Applied repeatedly, it could just destroy the mountain.

An alternative approach is fumigation based on a Wounding Flash Frost Blizzard. Ideally, you make it Violated as well to prevent any pesky healing.

[Calthropstu]

Is it specifically anti-scrying and not general anti-divination?
If so, there is the locate city bomb, though that may not play well at every table.
The city is inside a mountain. No line of effect. LCB simply fails here.


"Professionals have standards!" - Sniper.

Okay, outside of freezing the core of the World, I'd make use of Widened Earthquake to undermine the structures around the walls of course, essentially creating sink holes. Other good options would be Elemental Swarm or Summon Elemental monolith for Earth and Magma Elementals, and use their abilities to move through earth to change the internal Magma Channels so that they channel through said Force walls, turning the area into a deathtrap.

Nice! I like this.


Some clarifications needed:
- Is this for a specific game? If so- what are the game specifics? Any more info on the opposition? On the party? (Classes, level, other resources)
- If it isnt for a specific game, still some specifications- For a published campaign setting? Level of magic in the world? Resources the party can attain? Still, more about the enemy and it's capabilities?
- Available resources in terms of source books and mags?

I know the question is about blowing it all up, but it is worthy to note that on the whole- just because an entrance is well defended, it doesn't mean you can't enter by subterfuge and deception. Is the inside defended just as well? Can the party get inside close to the bbeg using disguise and bluff/ illusion and enchantment spells, by which they may bypass most opposition? (If someone is getting out, they can be caught, interrogated, threatened/ blackmailed, impersonated and more).

It's more as back story. All of this already happened. The bbeg was defeated when the hero brought his mountain fortress down upon him. I want a rules legal way of doing this.

Since I am both the gm and world creator, pretty much anything goes, though I won't delve into dragon mag. Or spheres. Personal preference.

Here's a nuke (https://forums.giantitp.com/showthread.php?621105-The-best-nuke). Applied repeatedly, it could just destroy the mountain.

An alternative approach is fumigation based on a Wounding Flash Frost Blizzard. Ideally, you make it Violated as well to prevent any pesky healing.

Interesting, though I hesitate to give this option to my players. Anything I can do, my players can do.

[Anthrowhale]

Interesting, though I hesitate to give this option to my players. Anything I can do, my players can do.
For something in the past, giving the players the outcome but not an explanation of the means seems very reasonable. Given that the means is a 20 level highly specialized build, it's also not super clear that they would take advantage of it even if they knew how.

[nedz]

Planar Engineering.

1) Open a portal to the Positive material plane
2) Open a portal to the Negative material plane
3) Leave the area, quickly
4) Boom

[gijoemike]

snip
There's an entrance but it is so well defended it'd be suicide.


No one ever cared about the entrance. There is a spell transmute rock to mud. Level 5 Druid/Sorc/Wiz. 2 2 10ft cubes of rock PER LEVEL become mud. As a 5th level spell you can make a wand of it. A single wand at minimum caster level can make 900 10" cubes of passage. The trick is it can only be 10" deep per casting. But each casting is a giant mudslide. Just cast it on a cliff face a few times and any sort of entrance or defensive structure is toast. Also that is 50 castings at 10" deep per cast. So 500 ft into the mountain is pretty structurally damaging.


Same wand will destroy the heat tubes of the geothermal plant.


Also
Getting into the fortress is very very easy at high level. Getting in practically unnoticed is not much more difficult but it would take a few more wands.

[Crake]

It's more as back story. All of this already happened. The bbeg was defeated when the hero brought his mountain fortress down upon him. I want a rules legal way of doing this.

Since I am both the gm and world creator, pretty much anything goes, though I won't delve into dragon mag. Or spheres. Personal preference.

You're the GM, you are the rules. Is there a reason why you want to take existing rules and twist them into a shape that vaguely resembles what you want instead of just making your own rules as the GM?


As a 5th level spell you can make a wand of it.

Wands are limited to 4th level spells.

[Psyren]

Earthquake can collapse caverns, and it's reasonable that under the right conditions it can collapse whole mountains. (https://www.giantitp.com/comics/oots0827.html) The biggest challenge would be getting in range of the load-bearing parts.

[ShurikVch]

Travel to the "roots" of the mountain in question, and cast Rockburst (Shining South)?

[Tvtyrant]

Wall of force lined up in space so the walls of force around the mountain hit them? It should compress the air between them to the point of nuclear explosion++.

Who knows what the interaction would be between the two walls other then that. Neither should be stopped or break, so it is up to you.

[satorian]

Iron Golem + Mattock of the Titans + time

If he hits a wall of force, have him programmed to go under it and undermine. Or give him a Rod of Cancellation to use on any pesky walls of force.

Alternatively, if he hits a wall of force, you now have line of effect for your locate city bomb, through his tunnel.

[One Step Two]

Okay, so let me paint a picture for you.

Imagine an active volcano slowly oozing lava out from an ill-formed caldera that looks like the jagged teeth of a hungry beast, around the peaks are temperamental storms caused by a strange phenomenon of floating rocks that defy gravity and conventional logic. In addition to this the side of the mountain itself is covered in deep fissures that intermittently shoot out super-heated gasses that sound like the gasping breath of a dying titan.

So, how did the fortress came to be this way? Through the use of Voidstone. (https://forums.giantitp.com/showthread.php?480986-The-Voidstone-Arsenal-For-when-you-really-want-stuff-gone)

The method involves first traveling to the Negative Energy Plane, and finding a large enough "field" of Voidstone. You first use Animate Object on suitable pieces of voidstone, then using Planar Bubble (reach spell metamagic to avoid touching them), and Plane-shifting them into the mountain, letting the errant pieces of Disintegration made into material stone cause untold chaos, they can also possible destroy the walls of force. However, the stone react harshly to the gravatic forces of the Geothermal energy, resulting in the mountain becoming a cursed ruinous place as described above.

[BaronDoctor]

Mineral warrior gets a burrow speed. Rock to mud, mud to rock, malicious use of fabricate (sensitive components turned into a statue of yourself), and you can do it with 5th level spells instead of higher level ones.

[Soranar]

flood it

control weather : downpour

enough water (and walls of rock to block off the exits) and most minions shouldn't last too long.

[gijoemike]

You're the GM, you are the rules. Is there a reason why you want to take existing rules and twist them into a shape that vaguely resembles what you want instead of just making your own rules as the GM?



Wands are limited to 4th level spells.

Thank you Crake for keeping me honest. I have screwed up. Potions cap at 3rd, wands at 4th not 5th. My plan would require staves of stone to mud and that would be far more expensive.

[Palanan]

Originally Posted by Calthropstu
…ant scrying….

So Michael Douglas is the BBEG?

:smalltongue:


Originally Posted by Calthropstu
The solution? Bring the entire mountain down.

How would you go about this?

Bargain with clans of xorn and thoqquas to undermine the fortress.


Originally Posted by Maat Mons
Since he's reliant on geothermal energy, you can defeat him by freezing the world's core.

This was actually my very first thought, but I had the general impression we wanted to save the planet.

[Ruethgar]

Create Element(Earth:Stone of Annihilation), then telekinesis it against everything. Alternatively, Black Sand, if your DM is realistic, any amount of it will decimate a planet without magical intervention.

Similarly, Dust of Dryness and Powdered Water are technically valid Prestidigitation creation items, as long as you blow it into the entrance from far enough away, you got a decent chance at a flood.

Unseen Servants aren’t bound by creature limitations, they technically encompass the whole of the spell area but act slightly like medium things. So if you have anything in sight past a wall of force to manipulate within a couple hundred feet that could give you an advantage, that is a potential, but unlikely, option.

War Fimbulwinter is a fun idea, technically the mountain would be taking the massive cold damage. Plus you cover the area in so much ice that anything alive suffocates.

[Biggus]

Since he's reliant on geothermal energy, you can defeat him by freezing the world's core.


Or you could go the other way and raise a (widened?) volcano (http://archive.wizards.com/default.asp?x=dnd/fw/20031017a) directly under his geothermal power source. If you get it in the right place, it should be spectacular to put it mildly.

[Rebel7284]

Interesting, though I hesitate to give this option to my players. Anything I can do, my players can do.

Erupt and Raise Volcano are fair, after all, they are 9th level blasting spells. They should at the very least do a fair amount of flashy damage when they are competing for spell slots with Wish and Shapechange.

However, if you specifically want to make the spell that blew up the mountain less accessible to your players, you can just make an epic spell. Kicks the problem down the road at least until your players get to level 21!

[Segev]

A monk/frenzied berserker/exotic weapon master with a double-headed exotic adamantine weapon can get enough attacks with sufficient average damage to destroy two 10-foot-on-a-side cubes of solid adamantine every round. This is significantly faster on mere stone. He also cannot die until he stops frenzying. The hero frenzied and burrowed through the mountain, undermining it personally.

[Dezea]

A monk/frenzied berserker/exotic weapon master with a double-headed exotic adamantine weapon can get enough attacks with sufficient average damage to destroy two 10-foot-on-a-side cubes of solid adamantine every round. This is significantly faster on mere stone. He also cannot die until he stops frenzying. The hero frenzied and burrowed through the mountain, undermining it personally.

While less flashy than the other way of doing it, I'd just love to be there for the moment of the grand reveal when the player discover, after infinite layers of secrecy, that the ultimate means of mountain-destroying was some crazied dude with a big axe.

[Kazyan]

Have your historical hero make a deal with the local Spirit of the Land (https://www.realmshelps.net/monsters/block/Spirit_of_the_Land), which is surely chuffed about the whole situation. Relevant at-will abilities include Earthquake, Move Earth, Soften Earth and Stone, and Stone Shape.

EDIT: For a coercive way to handle it, a Spirit of the Land is a valid target for Greater Spirit Binding, the 8th-level Wu Jen spell.

[AvatarVecna]

It's more as back story. All of this already happened. The bbeg was defeated when the hero brought his mountain fortress down upon him. I want a rules legal way of doing this.

If you wanna flex on your players, tell them the one responsible did it via the Profession (Miner) skill. It's sooooo much slower than smashing your way through, it's sooooooo much harder to get even relatively useful speeds, and AFAICT there's no actual benefit. The closest I could guess is that Profession (Miner) involves digging the tunnel in such a way that it won't cause a collapse above it, but that's the opposite of what we want. DC 15 gets rid of 1 5ft cube over 8 hours. Every +5 over that DC gets you another cube. Ooooooooh. Volume is doubled per size above Medium you are (for a theoretical max of 32 cubes at DC 15 for a Colossal+ creature).

There's a limit on how many creatures can aid you when you attempt such a check, but it's a joke: a successful aid attempt gives +2 to the main check, but if that person were making their own check and could only hit DC 10 anyway, that'd still be the equivalent of +2.5 to the main check - and as their bonus improves, their ability to clear tunnels on their own advances quicker than their ability to assist you in clearing your tunnel.

If we were to compare Profession to attacking the walls of the mountain directly, we can see how advantageous it is to just let damage handle things. DC 15 check from a colossal+ creature gets rid of 32 5x5x5 cubes. This is equivalent to 8 hewn stone walls, which would have 7200 HP in total. Since this is done per 8 hours, this means we have to manage an average of 1.5 DPR, and an additional 1.5 DPR per +5 DC the colossal+ creature can hit. A dire pick wielded by your average Commoner 1 is the equivalent of a DC 25 check from a colossal+ creature. But we can get a better weapon, and a better wielder, than that.

Orc Barbarian 10/Frenzied Berserker 10

Attributes: Str 40, rest don't matter:
18: Base
4: Race
5: HD
5: Tome
6: Magic Item
2: Permanency'd "Enlarge Person"

Feats:
HD 1: Power Attack
HD 3: Cleave
HD 6: Intimidating Rage
HD 9: Ruinous Rage
HD 12: Exotic Weapon Proficiency (Minotaur Greathammer)
HD 15: Improved Critical (Minotaur Greathammer)
HD 18: ? (dealer's choice?)


Weapon: Adamantine Minotaur Greathammer (Enhancement +1, Haste, Collision) which also has a property built in stolen from the Mace Of Ruin (the ability to crit objects and constructs). This ability costs ~20k given how epic enhancement bonuses are priced.

Weapon has "Greater Mighty Wallop" cast on it, such that its base damage is 12d6. Weapon has had Greater Magic Weapon cast on it, changing Enhancement to +5.

PC has had an Enlarge Person spell cast on them and permanency'd.

PC has purchased a manual of Str +5.

PC has purchased a belt of giant strength +6.


Certain attacks are especially successful against some objects. In such cases, attacks deal double their normal damage and may ignore the object’s hardness.

Big hammers are the go-to for smashing stones and mining. The only thing perhaps more appropriate would be a pickaxe. Let's suppose this qualifies for the double-damage. Per stacking rules, this means x2 damage on hits and x5 damage on crits.

Attack Routine: +19/+19/+14/+9/+4
+20: BAB
+15: Str mod
+5: Enhancement
-1: Size
-20: Power Attack


Damage: 12d6+112
12d6: Base
+22: Str x1.5
+5: Enhancement
+5: Collision
+80: Power Attack

You attack the wall in front of you 5 times per round. You miss 20/400 times (dealing 0 damage), hit 304/400 times (dealing 24d6+224 damage, avg 308), and crit 76/400 times (dealing 60d6+560 damage, avg 770 damage). Realistically, 3 hits, or hit+crit destroys a wall section. We get about 4 hits per crit, so that eyeballs as "for every crit we get, two wall sections get destroyed". Over the course of 8 hours (4800 rounds), we'll attack 24000 times, and thus crit 4560 times over the day's work, and thus destroy 9120 sections of wall. Each section is 10 ft x 10 ft x 5 ft, so that's ~4.5 million cubic feet of stone you destroy on your own in an 8 hour shift.

Half-Dragon template is easily LA Buyoff'd and XP River'd by this point.

Frenzied Berserker doesn't have an official epic progression but we could make one pretty easily. The part we care about is that it'd end up with a -1/+8 damage tradeoff, and higher BAB.

We'd get 7 epic feats to spend on Great Strength, although FB epic feats couldn't contribute there so 7 is the limit. HD gives another 5. Item limits give another 6 (well, theoretically infinite, but let's say another 6). Weapon enhancement can just be built at +18 (again, theoretically infinite but...eh). We've removed haste, which reminds me...

For ****s and giggles, a pile of continuous spell effects:
Enlarge Person is replaced with Giant Size CL 19 (Size bonus +32 now)
Greater Mighty Wallop is replaced with Earth Hammer
Divine Power gives us BAB +40 and other less important things
ditch Greater Magic Weapon entirely, we can afford a real weapon now
Choose Destiny, for 2d20k1 on all d20 rolls
Sakkratar's Triple Strike, essentially two haste attacks

New numbers:

Attributes: Str 96 (+43)[list]
18: Base
12: Race
10: HD
5: Tome
7: Epic Feats
12: Magic Item
32: Giant Size

Attack Routine: +53/+53/+53/+48/+43/+38
+40: BAB
+43: Str mod
+18: Enhancement
-8: Size
-40: Power Attack


Damage: 16d6+407
16d6: Base
+64: Str x1.5
+18: Enhancement
+5: Collision
+320: Power Attack

Hit deals 32d6+814. Hits essentially destroy a wall section every time. Over the course of 400 attacks, we'll miss 1 time and hit/crit 399 times. Over the course of 8 hours, we'll attack 28800 times, and thus destroy 28728 sections. Again, this is 10x10x5 cubic ft, so total destroyed is 14.36 million cubic ft over the course of an 8 hour shift.


Collateral Damage: If you destroy a 10-foot-by-10-foot section of wall, you weaken nearby walls. Wall sections to either side of the destroyed wall take 10% of their total hit points in damage, and walls above take 50% of their hit points in damage. Figure out the total damage, then subtract the wall’s hardness. For example, if you destroy a 10-foot by 10-foot section of masonry wall (90 hit points) on the first floor of a stronghold, the wall sections to either side will take 1 point of damage each (9 – hardness 8). Masonry wall sections above the destroyed section take 37 points of damage (45 – hardness 8). Collateral damage is cumulative; a wall section on the third story takes damage when the first story section below it is destroyed, and again when the second-story section below it is destroyed.

Characters standing near a wall when it’s destroyed risk getting caught in the rubble, unless the destruction was caused by something such as a disintegrate spell. Characters within 5 feet of a wall section when it’s destroyed suffer 1d6 points of damage, plus an additional 1d6 points for every 50 hit points of the wall section, to a maximum of 10d6 (Reflex save DC 15 halves).

Those who fail their Reflex saves are pinned beneath the rubble, and they take 1d6 points of subdual damage per round. Pinned characters who fall unconscious from subdual damage must make a Constitution check (DC 15) or take 1d6 points of normal damage each minute thereafter until freed or dead.

Underlined for emphasis. Conclusion: destroying the lowest two sections of a mountain will cause all the mountain directly above those sections to collapse as well. Combine this with any method of attacking squares (either the above stupid hammer builds, or something more reasonable like big AoEs) to carve a path through the mountains that goes all the way up.

1) An object weighing 1 lb that falls at least 1400 ft (which takes about 9.33 seconds to fall) will deal 20d6 damage on impact (avg 70).

2) Hail forms 20000 ft up.

3) Fimbulwinter is an 8th/9th lvl spell that takes 10 minutes to cast, affects an area 15+ miles in radius, and lasts 4d12 weeks (avg 182 days). Let's "Extend" it to be 8d12 weeks (avg 364 days).

4) Fimbulwinter can create hail and snow. While the only hail example given is 1-inch, it's not a stretch of the imagination to say that Fimbulwinter is capable of delivering hailstorms as frequent and as absurd in severity as its snowstorms. It's the winter to end all winters, literally.

5) There is real-life precedent for 1-lb hail. It is perfectly reasonable for Fimbulwinter to be capable of this even if it's not explicitly listed.

Conclusion: After 2.6 million rounds of the weather being absolutely awful, a not-insignificant portion of those rounds will feature hail falling all over the mountain, with each big hail dealing 20d6 damage to the stone (avg 62 damage after hardness, maybe halved then hardness'd for 27 if you decide ice is more likely to shatter itself on impact than truly hurt the stone). Even then, that's 33 hail impacts to destroy a 10x10x5 section of the mountaintop. How long before 33 big hail hit the same 10x10 surface area?

Assuming we average 1 big hail per 10 minutes (since it's not hailing all the time, and while lots of hail will hit each spot, not so many big hails will hit), each 10x10 surface area section will get hit by 52416 times, eroding 1588 layers off the mountain, each 5 ft deep. Everything within 15+ miles of the fortress will be ~8000 ft shorter than it was a year ago when the Fimbulwinter was cast. This method definitely takes some time, but it's neat.

[rel]

Destroying a mountain seems appropriate for epic spellcasting.

Use the conjure seed to create a big sphere of something heavy above the mountain and let gravity sort it out.

Alternatively, if you rule that lava is creatable with the conjure seed or a combination of conjure and energy, create a large amount of lava beneath the mountain and let pressure push it upwards

[Vaern]

The city is inside a mountain. No line of effect. LCB simply fails here.


Locate City's long description indicates that it's capable of detecting things underground, even directly beneath a caster on the surface above it. Line of effect shouldn't be an issue, especially if the DM is letting you get away with LCB cheese to begin with.

[Bronk]

I would suggest an orchestrated planar slippage if you wanted to keep it improbable but not impossible for lower level NPCs to accomplish. For something more flashy, have some epic wizard hit the mountain with Proctiv's Move Mountain to slice the mountain right in half, then blast the helpless innards with a couple of oversized hellballs or something.

[ShurikVch]

Nuke it.
Call Weaponry (https://www.d20srd.org/srd/psionic/powers/callWeaponry.htm): Nuke? :smallamused:


Destroying a mountain seems appropriate for epic spellcasting.
Sandstorm have the Volcano epic spell

[unseenmage]

Bringing the Sun to Earth (https://youtu.be/J0ldO87Pprc) is my go to solution. Methods of accomplishing such vary. Usually requiring a gate, portal, or ring gates to the sun then getting spell effects to the other side.


Spamming Fabricate + Animate Objects or Minor Servitor to transform the surrounding earth and stone into creatures capable of digging out even more suits my taste too.

Antigenesis says it crumbles both natural landforms and constructions.

Take a colossal object, maybe a literal boatload of Quintessence, hit it with Shrink Item, then with Animate Objects, then hit it with the Minute Form spell.
After Minute Form brings it to fine size activate Shrink Object.
Make a multitude of these.
Give them all Contingent Dispel effects and send them in then release them all at once inside the structure.
It isn't nuked, but it is time locked from the inside.

[ShurikVch]

True Creation: antimatter (https://en.wikipedia.org/wiki/Antimatter)...

[Melcar]

Planar Engineering.

1) Open a portal to the Positive material plane
2) Open a portal to the Negative material plane
3) Leave the area, quickly
4) Boom

What would that do? Are you thinking it’s matter vs antimatter this meaning annihilation?

[stack]

Sneak brown mold into the geothermal power plant? Not a complete solution, but amusing and could disrupt the power supply.

[Calthropstu]

A lot of these solutions are quite creative but I am describing in game why a mountain was basically blown in half. I was basically asking for a "how."

[epos]

A lot of these solutions are quite creative but I am describing in game why a mountain was basically blown in half. I was basically asking for a "how."

I don't think you need a particularly precise answer, honestly.

"The Great Heroes of Old sundered the mighty structure, with both Steel and Spell." will probably be enough to answer the bare question.

What might be fun is to have differing accounts of how it was done, depending on who the party asks, or where they might be. Perhaps some aspiring wizard would say that a mighty mage turned the mountain into a volcano, or a guardsman might say that a mighty warrior swung their axe so hard, the mountain was split in twain. Maybe even some small hamlet claims to have been the place where one of these heroes of legend was born, and thus have their own tale spinning their local legend into the primary figure of this event.

What you're discussing seems to have been fairly important to the setting, so while it might be good to have a definitive answer, if it happened a decently long time ago, perhaps the truth isn't so easy to find.

[Calthropstu]

I don't think you need a particularly precise answer, honestly.

"The Great Heroes of Old sundered the mighty structure, with both Steel and Spell." will probably be enough to answer the bare question.

What might be fun is to have differing accounts of how it was done, depending on who the party asks, or where they might be. Perhaps some aspiring wizard would say that a mighty mage turned the mountain into a volcano, or a guardsman might say that a mighty warrior swung their axe so hard, the mountain was split in twain. Maybe even some small hamlet claims to have been the place where one of these heroes of legend was born, and thus have their own tale spinning their local legend into the primary figure of this event.

What you're discussing seems to have been fairly important to the setting, so while it might be good to have a definitive answer, if it happened a decently long time ago, perhaps the truth isn't so easy to find.

Well, the bbeg found a journal left by the previous bbeg detailing how to harness geothermal energy and channel it into powerful weapons... So the quest is for "how the hell was the previous guy able to obliterate an entire mountain?"

Both the pcs and the bbeg have an interest in finding out as the bbeg is basically following a similar path.

[Biffoniacus_Furiou]

A lot of these solutions are quite creative but I am describing in game why a mountain was basically blown in half. I was basically asking for a "how."

The heroes found a sword that could sunder walls of force. They took it to a demiplane where transmutation effects are exponentially more powerful but also reversed, and made the sword bigger using Shrink Item. Then they just plane shifted the sword back to the material plane several hundred feet above the location, allowing its descent and weight to split the mountain asunder. The spell enlarging the sword was dismissed and they retrieved it, and the demiplane they used had collapsed long ago.

[Jazath]

The big bad is in a gigantic fortress deep on the inside of a mountain. His engines of war are fueled by geothermal energies. Anyone trying to go in would be suicide. The entire fortress is covered in anti teleportation, ant scrying and butressed by permanent walls of force. There's an entrance but it is so well defended it'd be suicide.

The solution? Bring the entire mountain down.

How would you go about this?

Once you bypass the Walls of Force,
Forecast calls for a Meteor Shower and Earthquake Spells.

And then Wish it all away~

[rel]

A lot of these solutions are quite creative but I am describing in game why a mountain was basically blown in half. I was basically asking for a "how."

The mountains defenses were designed to repel a direct large scale assault. A small group of specialists were able to infiltrate the mountains lower levels and set off a catastrophic overload of the geothermal generators.

[Calthropstu]

The mountains defenses were designed to repel a direct large scale assault. A small group of specialists were able to infiltrate the mountains lower levels and set off a catastrophic overload of the geothermal generators.

Hmmm. Possible.

[Segev]

Hmmm. Possible.

Has the added benefit of being a dungeon crawl worthy adventure in its own right, and thus something you could run as a prologue or as a flashback with pregen characters later in the game.

[Mordante]

Bring Atropus to the world awaken and unleash.

[Bronk]

A lot of these solutions are quite creative but I am describing in game why a mountain was basically blown in half. I was basically asking for a "how."


Well, the bbeg found a journal left by the previous bbeg detailing how to harness geothermal energy and channel it into powerful weapons... So the quest is for "how the hell was the previous guy able to obliterate an entire mountain?"

Both the pcs and the bbeg have an interest in finding out as the bbeg is basically following a similar path.

Then how about 'someone blew up and/or used the powerful weapons, or the weapons were made wrong'?

Otherwise, I suggest letting the players come up with their own theories, then mostly going along with whatever they come up with, just one upping it a bit and adding a twist.

If they come up with 'they infiltrated the guys supply line, and put someone's familiar in a box along with a bag of holding, a portable hole, and a map to something explodey', you can just say 'Yes, only you get in there, and the geothermal harnesser works on ground up angel kneecaps and the sacrifices of the loved ones of powerful PCs, all of whom are at ground zero!'

[noob]

The geothermal power generators might actually have disfunctioned and exploded spontaneously due to shoddy crafting then the ancient bbeg blamed the ancient heroes

[rel]

The geothermal power generators might actually have disfunctioned and exploded spontaneously due to shoddy crafting then the ancient bbeg blamed the ancient heroes

As long as the current heroes get to perform an infiltration and sabotage dungeon crawl of their own when the current BBEG decides that building a second death star is a brilliant plan it's all good.

[Efrate]

Find sea of lava on plane of fire. Cast gate. Ideally from inside but anywhere works. Walls of force turn into funnels. Plane of water would work as well. Might take a few castings.

[unseenmage]

Find sea of lava on plane of fire. Cast gate. Ideally from inside but anywhere works. Walls of force turn into funnels. Plane of water would work as well. Might take a few castings.

By default unattended objects won't pass through a gate spell gate.

However, in the Underdark book there are variant portals that transport water. Easy enough to make one transport lava instead.
Just Wish the portal into existence as a magic item if you must.