Obscuring Mist, Abyssal Ghouls Chamber
The only entrances/exits to this chamber are arcane locked iron doors with small barred eight inch square barred windows (2inches, hardness 10, 60hp, break DC 38). These doors will only open by using a special magic key found somewhere else in the dungeon.
This chamber is eighty feet square with a fifteen foot high ceiling. The walls, floor and ceiling of the room are covered in a dark clay "plaster" a foot thick. There are humanoid bones stuck in the plaster (skulls and limb bones). Behind the clay plaster are walls of dark stone. Here and there, some of the clay plaster may have fallen away, revealing the stone walls behind.
The entire chamber is filled with magic mist that acts as permanent obscuring mist spell. The vapor obscures all sight, including darkvision, beyond 5 feet. A creature 5 feet away has concealment (attacks have a 20% miss chance). Creatures farther away have total concealment (50% miss chance, and the attacker cannot use sight to locate the target). The volume of mists, and the fact that it is continually being created and replenished makes it impossible to clear away the mists with a gust of wind spell. A fireball, flame strike, or similar spell burns away the fog in the explosive or fiery spell's area. A wall of fire burns away the fog in the area into which it deals damage. This will clear the fog in about a twenty foot area for only one round, then the mist rolls in and fills in the space.
There are large stone pillars in this chamber (every twenty foot space) covered in the same dark clay with embedded skulls. These pillars are enchanted to continually produce obscuring mists. Mist pour from the mouths of multiple skulls on the pillar as if casting obscuring mist once per round. The mists flow away from the pillar at a speed of five feet per round.
Hiding in the mists of the chamber are multiple abyssal ghouls (fiend folio page 12, hide +20, init +7, spring attack, sneak attack bonus, blind sight, scent = can sense creatures within 90 feet). The abyssal ghouls will instantly sense anyone entering the chamber and move in to attack. They will use their spring attack and sneak attack abilities to come out of the mists, attack and then disappear into the mists again. They will toy with their victims attacking only every other round or so.