Demonarch Gallery is a massive underground hall split into two levels, partially supported by massive scorched pillars. Around the edges of the hall are a variety of rooms, chambers and facilities.
But the name isn’t just a scare tactic. The hall has been used to summon foul creatures from other worlds for so long that the interplanar rifts here can occur nearly spontaneously. Whenever a spell is cast within the hall, roll 1d30 – if the result is the level of the spell cast or lower, then a gate opens between two of the pillars allowing entry to some foul creature from the other side. Spells cast in the adjoining areas are much less likely to trigger a rift – roll 1d100 instead of 1d30.