Zakkencrag is a dwarven holdfast in the Underdark, not far from the drow city of Erelhei-Cinlu. Until recently, the city was ruled by a king advised (via possession) by ancestral spirits, but now a cranium rat hive known as the Chorus of Minds is in charge.
Hidden over a subterranean river through architectural ingenuity, the stronghold is set up almost vertically, with shafts and fortified staircases running up-and-down between its chambers. The city was built around a series of ancient tombs, with several crypts converted into living spaces and connected to this greater network. A sizable deposit of soul gems runs through the surrounding rock, and is said to be what powers the Seat of the Ancestors, as well as many of the magic items created by the Forgestewards. A massive glowing sphere hung in Zakkencrag's central shaft, its light catching on these mineral veins and illuminating nearly the whole town, but was replaced by a device known as the Prismatic Percolator, which created a psychic field that blocked out the voices of the Seat of the Ancestors and amplified those of the Chorus of Minds.
Aside from the dwarves, a mixed population of gnomes and xvarts also exists around and within the fortress, although they are heavily discriminated against, the dwarves believing that these races are "privileged" simply to live under their protection.