The Underworld is the collective name used for the countless kilometers of deep tunnels, chambers, pits, and caverns that lie beneath the surface of The Whorl. The sorts of caves or mines worked by surface worlders for raw materials don't count. The true Underworld is a place eerie and strange, less cave than corridor; less cavern than facility. It is said that in the deepest rooms of the Underworld there are great transparent portals set into the floor through which one can perceive the Endless Void in all its maddening majesty.
The Underworld is clearly a built place, constructed for the use of people, yet no people live here aside from the dark elves, servants of the god Yama who claims the Underworld as his Realm. Others have passed through, brave explorers or desperate refugees, but intruders tend to be found and driven out eventually. Nevertheless, the Underworld is vast, and the dark elves are relatively few in number. They are not the only peril that awaits those foolish enough to attempt to plumb Yama's secrets. The Underworld is full of strange and incomprehensible machines performing unknown and often dangerous functions. Monsters make lairs down here far from the persecution of the surface. Even stranger dangers lurk far from Civilization.
Only the bravest or most foolhardy venture here, and only Yama knows its secrets.