The Kingdom of Light
A vast network of subterranean caverns beneath the Westreach. There are numerous caves dotted all over the surface that allow passage between the Underdark and the surface world. Various subterranean races are known to inhabit the Underdark, waging their own wars and subterfuges. Those known to the surface include the dark elves known as the Drow, and the sinister octopoid psionic menaces known as the Illithid.