Rope Trick Bunker of Doom
A little-known tactic in 3.x D&D, centered around the Wizard Spell, Rope Trick. Because the spell creates a 3'x5' extradimensional space, it can be used to bypass thin doors and walls, but the bigger use of this spell is to create impenetrable rest areas that require neither guards nor sleeping shifts, and which allow for parties to stop, prepare, and plan, even in the middle of an enemy's invincible doom fortress. The extradimensional space holds 8 people by default and lasts long enough for a full-night's sleep at 8th level (4th level with extend spell feat) or higher, meaning the only difference between this and Magnificent Mansion is that this doesn't have butlers or food by default - and is a 2nd Level Spell.
Note: Anything that can see invisible (don't forget the 2nd level spell) will see the dimentional window you opened. The DM will likely have an ambush waiting for you or if they have had enough of your bullshit, setup an ambush and cast dispel.