Lair construction and the problem with wall spells.

[Mathius]

I am bbeg and I want my lair to be difficult to penetrate.

I start with a teleport trap over the whole thing. To protect the horizontal edges I can lair walls or force and fire or even a go all out with a prismatic wall. There are many other fun walls as well if once can find a way to make them permanent.

This unfortunately leaves the top and bottom of my lair vulnerable. Mundane defense are not going to stop those pesky adventures. Earth glide lets them come up form under of down from above with ease and then the simply need to bash through a hard wall.

Would gravity sphere allow me to make horizontal walls? Short of dispelling can you get through a blazing rainbow?

[Kayerloth]

Difficult to penetrate by whom? Or more exactly by what levels/capabilities of whom?

How much wealth are you willing to blow ... i.e. That is a lot of wealth (even for PCs) to cover most lairs with Teleportation Circle traps? And where are these traps sending folks? Also sounds as if you've already figured away to keep those teleport circles from annoying your minions and slaves, yes? (since those traps teleport anyone standing in them or have been made relatively obvious)

Frankly both the Walls and the Teleport Traps sound more annoying than threatening or effective for the wealth needed to make permanent. My Loremaster, for instance, might just decide to drive you into bankruptcy by destroying your barriers, let you replace, destroy again >>(rinse repeat till you run out of funds to replace or elect not to replace).

Gravity Well - I see no reason in the description why Gravity Well would eliminate or alter the (by RAW) vertical requirement of any Wall spell. The spell changes the strength not the relative direction of gravity near as I can tell.

Blazing Rainbow - Any reason to believe from the text you can't just walk (move) through it? It seems to only effect those who are resisting being moved from the bridge version. The spell does seem to lack some clarity however (or a lot of footnotes). Nothing, for instance, says those effects apply to someone being Bull Rushed in the direction of the bridge vs off the side (and it's hard to say, for me, if that is RAI or not).

[DM_Blake]

By the time a BBEG can fill a lair with teleport traps and prismatic walls, why doesn't he just make his own plane and live there? Nobody will even know how to find it, and you sure cannot earthglide into it.

[DM_Blake]

Or for a different kind of answer, the difficulty and expense and perhaps even impossibility (without house rules) of making an impenetrable lair leads us to these conclusions:

1. PCs are supposed to be able to find a way to get to the BBEG. It's more fun that way.
2. BBEGs actually DO have a reason to hire guards and place them all throughout their lairs - guards are cheaper and more efficient and even more possible than the stuff the OP wants to do.

So place traps and wards around much of the lair, put the BBEG inside a space that has no doors or physical entrances - even he has to teleport or earthglide into his special private sanctum. Guard it with a teleport trap and have the BBEG animate a bunch of greater shadows to stay in the walls and attack anyone (else) who tries to earthglide into the lair. How embarrassing for an earthgliding party to have to fight incorporeal undead they cannot see or even attack while they are being drained 1d6 STR per hit, no defense, no AC, no fighting back.

[Kayerloth]

That's where knowing your party comes into play when designing a BBEG lair vs your party at high levels of play.

Passwall, Phase Door, or even Disintegrate will blow/bypass physical walls full of incorporeal undead. Toss in Death Ward and Sunburst when you know the BBEG trick. (Merely as an example, not saying DM_Blake's idea is a bad one as it's not)

Dispel Magic and/or Disjunction make very short work of Teleport Traps and many of the various Wall spells. While Arcane Sight, True Seeing and various Divinations (and plain old skill) can aid in detecting the presence of such barriers/traps.

The planar barrier surrounding your very own demiplane much more difficult but even it is a planar boundary nothing more, nothing less and spells can breach those as well but it does mean the GM better have a very solid grasp of what they consider the metaphysics of their world.