Making an impenetrable room

[InvisibleBison]

I've been spending some time over the past couple days contemplating how one would go about making a room that no one is able to enter (at least, without using wish). I think I've gotten a reasonably secure approach, and I though I'd post it here to be critiqued.

To carry out this procedure, you need to have 11th level wizard spellcasting, 6+ levels of dweomerkeeper, the Initiate of Mystra feat, and the ability to use a 9th level wizard scroll and a 6th level cleric scroll.

The procedure is as follows:

Use a scroll of genesis. Set the new demiplane to have no gravity and (if you're able to choose the time traits) timeless with respect to magic.
Use a scroll of forbiddance, reducing the affected area to a 10 foot cube.
Cast antimagic field. This lets you use the Initiate of Mystra feat to make all subsequent spells function in an antimagic field. Repeat this step as needed (the procedure takes several days).
Cast two walls of force, parallel to each other and tangent to the forbiddanced area.
Cast a supernatural spell dark way (SpC p. 58), anchored on the walls of force from step 4 and positioned to be on the edge of the forbiddanced area. This is the bottom half of one of the walls of the room.
If not operating on a timeless plane, cast supernatural spell permanency on the dark way. (This is the most questionable part of the procedure; however, given that permanency says that it can be made to apply to other spells and it can apply to wall of force, I think it's reasonable.)
Repeat the previous two steps (previous three steps if not operating on a timeless plane) to create the top half of the wall.
Repeat the previous three steps (previous four steps if not operating on a timeless plane) to create the other three walls.
If operating on a timeless plane, dismiss the anchoring walls of force.
Cast another two walls of force parallel to and right up against the sides of the room.
Cast another supernatural spell dark way, anchored on the walls of force, to form half of the ceiling of the room, applying supernatural spell permanency if necessary.
Repeat the previous step (previous two steps if not operating on a timeless plane) to form the other half of the ceiling.
Repeat the previous two steps (previous three steps if not operating on a timeless plane) to form the floor of the room.
If operating on a timeless plane, dismiss the anchoring walls of force.


Teleportation and planar travel to the inside of the room is blocked by forbiddance. Dark way is impenetrable, like a wall of force, but lacks wall of force's vulnerabilities. The only way through a dark way is to exceed its weight capacity, but as the room is located on a plane with zero gravity, no creatures or objects have any weight. As the dark ways are supernatural effects they can't be dispelled or disjoined, and as they were cast by an Initiate of Mystra they remain functional in an antimagic field.

If you see anything here that doesn't work, or if you can think of a way to bypass these defenses, please let me know!

[Bucky]

Planar Bubble is the obvious way in; use it to enforce normal gravity and overload the ceiling.

[Segev]

Build the room identically on the Ethereal and the Material planes.

Make the room at least 15 feet on a side; more is better. You want the "usable" part of the room to be at least five feet from the exterior of it. More is, again, better, because larger incorporeal creatures can penetrate deeper without ceasing to be adjacent to the exterior. You can possibly do this just by making the exterior walls on all six sides that big.

Fill the Material version with pure diamond, fabricated to be perfectly clear and to encase everything in the room perfectly.

Fill the Ethereal version with pure metal. Adamantine is best, but iron will do, as will anything else. Preferably something hard to damage or corrode.

Use Nystul's magic aura to make the interior of the room register as having Abjuration, and the walls radiate Evocation. When people approach its door on the material plane, they see into the room, and run into what appears to be a smooth wall that, upon magical examination, radiates evocation. Clearly, a wall of force or a large forcecage. If they attempt to teleport inside, they take damage as they're shunted back out. That Abjuration effect in there is mighty, indeed! If they think to try becoming incorporeal, they find they can only go in five feet before an inner barrier hits. Now, if you haven't put a real wall of force up to prevent this, they may start to suspect something's up, but it still will be confusing.

To access the chamber, you go to the ethereal plane and cast ironguard, which lets you pass through the nonmagical metal you've filled the chamber with. From the ethereal, you can see into the material, so you can see the material chamber just fine even though you're blind to anything going on in the metal that surrounds you. You're not incorporeal, so the usual rules forbidding ceasing to be adjacent to the exterior don't apply. Ironguard just lets you ignore the metal's physicality.

Now, anybody who knows the trick can do this, so you've not secured it against other effects. Also, dedicated destruction can carve its way in.

You may need to pull things from the material to the ethereal to pull them out, too.

[InvisibleBison]

Planar Bubble is the obvious way in; use it to enforce normal gravity and overload the ceiling.

You know, I was actually looking at planar bubble while designing an earlier version of the room; I feel kind of silly for having forgetten about it. But it's possible to overcome - put a reverse gravity trap inside the room. Whenever someone touches the outer wall, the trap will trigger. Normally, this won't do anything, but if gravity has been introduced everyone will fall away from the walls and be unable to pass through them. Flying creatures won't be affected, but a control winds trap set to trigger at the same time will blow back them back. Alternatively, you could put walls of force just inside of the dark ways, but that's not such a good approach, as sufficiently heavy rod of cancellation would be able to bypass the dark way and destroy the wall of force.

[Bucky]

How does the reverse gravity spell interact with subjective gravity?

[InvisibleBison]

How does the reverse gravity spell interact with subjective gravity?

I think reverse gravity would cause you to fall opposite the direction you chose to be down, which might cause some problems at first but subsequently would make no substantial difference.

[Khedrac]

5. Cast a supernatural spell dark way (SpC p. 58), anchored on the walls of force from step 4 and positioned to be on the edge of the forbiddanced area. This is the bottom half of one of the walls of the room.
...
9.If operating on a timeless plane, dismiss the anchoring walls of force.
Permanent or not, as soon as you remove either anchor from one of the dark way bridges, that spell fails - further, because it explicitly is anchored to two objects, they cannot be substituted by another object after the spell is cast.

A dark way must be anchored at both ends to solid objects, but otherwise can be at any angle.
Personally I would question if a wall of force is even an object - it is a spell effect (riverine weapons not withstanding).

[InvisibleBison]

Permanent or not, as soon as you remove either anchor from one of the dark way bridges, that spell fails - further, because it explicitly is anchored to two objects, they cannot be substituted by another object after the spell is cast.

Personally I would question if a wall of force is even an object - it is a spell effect (riverine weapons not withstanding).

You're right. I got confused by the next sentence, but the anchors have to stay put even after the spell is cast. I guess this idea doesn't work after all. Oh well, back to the drawing board.

[Telonius]

This is an extremely obscure source, but (as far as I can tell) there's no way to overcome it except for an Antimagic Field. The Planeshifter prestige class from Manual of the Planes has "Planar Area Swap" as its 9th-level ability. It's a Spell-like ability, so Antimagic would foil it. But that aside, using it means that an area of up to 100 feet in radius (centered on the planeshifter) switches places with another plane of the Planeshifter's choosing. The whole defensive apparatus can be switched places with an equal-sized piece of the Elemental Plane of Air.

The truly crazy thing is that there is no mention of a daily limit on this ability.

[icefractal]

How about:
1) Make an exactly 10' cube demiplane.
2) Get an awakened Gelatinous Cube minion.
3) Give it a Ghost Touch Amulet of Natural Attacks (may require a level of Monk, but IMO a cube's slam attack is already its whole body).
4) Give it a size-reducing item.
5) Set up a permanent telepathic bond with it.

When you want to enter the room, contact the cube and have it shrink itself. Until it does, there is literally no space for anything else to occupy, not even incorporeal things. I'm not even sure if Wish would overcome that, or what would happen if it did.

[Oberron]

I've been a big fan of using a weird stone. Once it's activated a bubble 1 mile wide can't be teleported into and any divine attempts automatically fail to give infomation on inside the bubbles

[ShurikVch]

Wall of Force can be passed by a Force Dragon (https://www.d20srd.org/srd/epic/monsters/dragonEpic.htm#forceDragon), or anybody who capable to do sufficient Escape Artist (https://www.d20srd.org/srd/epic/skills.htm#escapeArtist) check

Forbiddance and any other kind of dimensional barriers could be bypassed via the Freedom of Passage spell (Sorcerer/Wizard 8, required githyanki silver sword as a focus; Dungeon #100/Polyhedron #159)