Underworld

The Underworld is an area where the ostracized sapient ghouls (as opposed to their feral bretheren) of Washington, DC live. It exists as a small city, complete with a bar, inn, clinic, and "stylist."

Most humans are tolerated, as long as they do not cause trouble. The Brotherhood of Steel are not welcome, however, as they tend to shoot Ghouls on sight.

It is located inside the Museum of American History. The museum was featuring an exhibit on the mythology of Hell and the afterlife during the time of the Great War, as most of the remaining exhibits (including the name of that section of the Museum as well) are all themed as such.

If you decide to blow up Megaton, then Moira Brown will survive and come to live in Underworld.

One of the robots in Underworld is named "Cerberus," who jokingly is referred to as the "Guard Dog." This is a reference to Greek mythology, where Cerberus was the 3-headed dog who guarded the gates to the Underworld.

Charon, the grouchy thug at the bar, also owes his name to Greek mythology, in which Charon is the pilot of the boat that takes dead souls across the underworld river Acheront into Hades. (Not Styx but Acheront!!! - Styx was a river of fire, no one could enter it)

Charon is an NPC who can join your quest.

There is a ghoul in the back of the top floor, main room, who has clean hair, unlike the other ghouls. He will give you a free haircut. This is because he says that other ghouls pay no attention to their appearance, and he is dying to work on someone who actually has hair.

Related Quests
Recruit Charon You Gotta Shoot 'Em in the Head