The Underdark

The Underdark is a subterranean network of caverns and tunnels that stretches across all of Ioro. Inhabited by the some of the strangest and deadliest creatures in existence, it is largely uncharted, and going there is considered tantamount to suicide. Some of the denizens of the Underdark include drow, illithid, duergar, svirfneblin, and kuo-toa.