A massive cavern underground that appears to be connected to multiple islands across the nightsea. Entry to the Underground can be achieved through the use of a special key that is inserted into a specific location on an island.

The primary city of the Underground. Undertown is a massive sprawling metropolis that is ruled by the Underground Lords and is the hub of illicit activities on Erth. It is hidden from the reach of the Scions and conducts trade with anyone willing to pay.