The Underdark

The Underdark is the name of the various caves, caverns, and tunnels below the earth which all connect to each other one way or another. It is technically possible to travel the length of the known world below ground, although much more difficult. The Underdark is populated heavily by monsters and drow elves. The drow are the foremost trade partners of Frostmarch, which has access to the best mines north of Goldscale Mountains. Some drow consider themselves affiliates with Frostmarch, and in exchange are given rights over some of the mines near the terran border.

Some areas within the Underdark are close to the Shadowfel plane, and occasionally undead creatures can be found, former denizens of the Shadowfel who shambled into the prime material plane.