The Underworld

The Underworld is a hellish, red-hot landscape which covers the entirety of the Earth's upper mantle. Vegetation cannot survive there, nor can any earthly creatures. It is home to many species of demon along with human cultists who have chosen to devote their lives to demonic pursuits. Its denizens live in towns of all sizes, made almost exclusively of the soil and stone of the region, and some live in ragtag cults with no fixed home.