any ideas for defending a sky castle???

[Joe dirt]

Hello all, joe dirt here, previously on a different thread i told u that our group took control of a flying island fortress (it has a control room where one can fly the island). we have been attacked by various foes trying take our island from us, a dragon, a powerful spell casting warrior, some slaad.

well, i am the wizard of the group and now that we have achieved the magical 7th level and i have access to the fabricate spell, my character is built around this spell and has the following skills to match, tinker tools, smiting tools, leather working tools, stone mason, carpentry. next level i plan on taking the skilled feat again to pick up alchemy, brewing, and glassblowing skills.... to make the world a drunker place. (and for the alcohol for flame throwers)

my current plan is to build intricate traps to protect the island and its control room from outside invaders, or even people that can teleport into the control room itself.

anyone wish to put there 2 cents in on what types of traps to include? where to put them? also what other ideas would u have me make? i am thinking of a hoist system to raise and lower large items and goods might be important, along with escape pods with parachutes.... but any other help would be appreciated... thanks

[Unoriginal]

Build siege engines and put them all around, below, and above the castle in a way that there is no dead angle in the castle's ranged defense.

[Lord8Ball]

You could try creating flying golems with laser beam eyes and create an apparatus using the power source that keeps the island afloat to create a laser from the bottom of the island as powerful or even more powerful than a hydrogen bomb. I got this Idea from Laputa castle in the sky, but some anti-air defense would be great. It may be beneficial to you to allow for some people to immigrate to your castle.

[StorytellerHero]

Vigilant surveillance of the surrounding region helps to secure a location.

A watchtower would be pretty normal for a fortress.

The earlier you can detect trouble incoming, the earlier you can prepare defenses.

[Scots Dragon]

For basic defence you're gonna want ballistae and well-defended spots to place archers for direct flying opponents on the edges of the island. While these aren't going to do much against really powerful enemies, they can prove somewhat bothersome to most foes on aerial mounts if nothing else.

Beyond that you're gonna want to use summoned monsters that can best take advantage of the island's natural environments. This includes earth elementals for on-land defence, and air elementals or other flying monsters for everything else. You might want to make these in the form of traps that spring upon an enemy entering a specific location, basically making your entire island into a dungeon crawl for any enemies you might have.

[Caelic]

Spellcasters capable of casting immobilization-type spells are lethal when properly used in aerial combat.

Other ideas:

1. A sphere of Programmed Illusions around the entire castle. The triggering condition is saying the command phrase "Engage the cloaking device!" When activated, the illusions project an image of empty sky. (If you want a longer duration cloak, create three nested spheres of such illusions. The outer sphere is activated by the phrase above, the middle sphere is activated by the outer sphere going dormant, and the inner sphere is activated by the middle sphere going dormant.)

2. A Forbiddance should go a long way towards keeping out certain types of unwelcome guests.

[Zanthy1]

Forbiddance (6th level) is going to be one of your best friends, cast in on the inner sanctum and nothing can teleport within. Combine that with Nondetection (3rd level) so they can't scry in. On top of that, I'd seal in the control room entirely. No doors at all (with the forbiddance spell too). That way the only way in is teleportation, and only you and those you designate can teleport in. Bonus, get a cleric to make a shrine in the control room to their deity and have them have word of recall (6th level) prepared for immediate summons of the party. Alternatively, use teleportation circle (5th level) as your method of entering and exiting the sealed sanctum.

[Hypersmith]

Forbiddance (6th level) is going to be one of your best friends, cast in on the inner sanctum and nothing can teleport within. Combine that with Nondetection (3rd level) so they can't scry in. On top of that, I'd seal in the control room entirely. No doors at all (with the forbiddance spell too). That way the only way in is teleportation, and only you and those you designate can teleport in. Bonus, get a cleric to make a shrine in the control room to their deity and have them have word of recall (6th level) prepared for immediate summons of the party. Alternatively, use teleportation circle (5th level) as your method of entering and exiting the sealed sanctum.

This is very solid. After all that the only way in and out for others is physical means, so having ways to dispel magic or hold person easily available is a good way to stop others from barging in.

[Cybren]

Build siege engines and put them all around, below, and above the castle in a way that there is no dead angle in the castle's ranged defense.

Don't build them so that they can point at the castle if taken by the enemy though

[SpamCreateWater]

Forbiddance (6th level) is going to be one of your best friends, cast in on the inner sanctum and nothing can teleport within. Combine that with Nondetection (3rd level) so they can't scry in. On top of that, I'd seal in the control room entirely. No doors at all (with the forbiddance spell too). That way the only way in is teleportation, and only you and those you designate can teleport in. Bonus, get a cleric to make a shrine in the control room to their deity and have them have word of recall (6th level) prepared for immediate summons of the party. Alternatively, use teleportation circle (5th level) as your method of entering and exiting the sealed sanctum.

This is a great spell. How big is the island?

Ask if you're allowed to use this homebrew (https://imgur.com/a/3cSLA) on fortresses and strongholds. We've allowed it in our campaign, but no one has the cash or drive to deal with it yet.
Unless any other Playgrounder has a better source???

The Symbol/Glyph of Warding spells are good for one-use traps. Guards and Wards. Hallow. Arcane Lock. Programmed Illusion.

[Chugger]

Magic self-cocking ballistas (giant xbows) or extra-heavy xbows on pivot mounts ringed by walls.

You could have a few heavy-duty "wands" or "staffs" (with charges) that are also pivot mounted and very very heavy - and each day at dawn recharge. They can shoot lightning bolts or magic missiles or w/e. A wild mix of stuff to shoot would be interesting.

Grappling and moving an attacker (or defender) to the edge and dropping them off is a strong tactic. What do the defenders do to prevent this? Do they tether themselves if they're, say, on a tower roof arming one of the above mentioned weapons or shooting arrows?

If you polymorph an incoming winged attacker into something with no wings, it will drop - the new form will take the first of the fall damage to 0 - then the rest of the damage will affect the creature's true form. Something to consider.

[Crgaston]

Lots of great ideas here!

Don’t forget spy glasses and net launchers.

[Sigreid]

The best defense is always hiding. The enemy can't harm what it can't find. Maybe a massive illusion of a cloud covering it.

[Throne12]

Glyphs of warding every were. Have them do different things like casting tidal wave to push enemies off the side. Some with hold person. Inside the fort cloud kill or walls like wall of fire, force. Get some hirelings or create some.

[ImproperJustice]

Since repelling flying invaders is hard.....
I would leave one or two “soft” entry points in your defense that lead into what should be an enclosed space that serves as a kill zone.

Then have a concealed sealable tunnel that allows your troops to counter attack any unboarded mounts that landed at the “soft point”.

[Easy_Lee]

This depends on the size of your castle and the way your DM rules it, but there's one spell that can ruin just about any flyer's day: sleet storm. If you can cast that into an object such that a henchman can use it on attackers from the control tower, they're failing "prone" for 20d6 damage.

[tieren]

In addition to the teleport in only control room, make a false control room somewhere on the other side of the fortress and defend it heavily with thick iron doors, glyphs of warding, traps, etc... Maybe even have some henchmen in there that sit at stations and operate knobs and levers.

Invading enemies may spend a good bit of time and energy going after the decoy.

[the_brazenburn]

Catapults that fire oozes, swarms of insects, mephits, and other things with nasty effects.

You could also have multiple spell gems casting Shield over the entire island at the same time.