Deep beneath the surface of the world lies the Underdark, a realm of endless labyrinthine tunnels and caverns where the sun never shines. The Underdark is filled with races and creatures too numerous to count or list, and and a few are too frightening to even mention.
An unusual magical energy the drow call faerzress pervades much of the Underdark. The origin of this mysterious arcane power is unknown. Legend claims it is an ancient elven magic dating back to the time when the dark elves were first exiled from the world above. The drow and other Underdark creatures use the properties of areas suffused with this energy to protect their settlements.