Underdark

Deep within the earth is the Underdark. One of the largest cities is Skullport. This city is kept a secret from of the surface world. Some rumors of it exist, but very few people on the surface would know how to reach it.   One of the secret entrances to Skullport from the surface world is located on Skellers island in the Naram River. It is guarded by the ghost of Nate Skeller, who was a human explorer who discovered this entrance. Once he died, his ghost haunts the entrance to scare people away.   Nate was working with the beholder, Xanathar, to locate Skullport. But Nate did not live long after they actually discovereed it. Xanathar went on to flourished in Skullport and is now one of its most powerful denizens.