The Ninth Circle

The Ninth Circle is a bar inside of Underworld Concourse which is in the Museum of History. The bar is owned by Ahzrukhal; it is rivals with another store in Underworld.

Unmarked quest: Hired Help
If you speak to Ahzrukhal, he will tell you that he holds the contract of employment (read: slavery) to a ghoul named Charon (also located in The Ninth Circle in the corner). Charon is bound to work for whomever holds his contract. Ahzrukhal also tells you that he dislikes having to compete with the other beverage outlet in Underworld, Carol's Place. He proposes that if you were to kill Greta, who works there, he would be willing to give you the contract to Charon. Alternatively, you can purchase his contract for 2,000 Bottle Caps (or 1,000 Bottle Caps if your Barter is high enough)

Trivia
"The Ninth Circle", is a reference to Dante Alighieri's The Divine Comedy. The first canticle is Inferno (Hell), which contains nine circles. The Ninth Circle is the circle of treachery. The fact that a character named Charon appears in Dante's Inferno to ferry Dante and Virgil across the Acheron river further suggests this connection.

It might also be a reference to Clive Barkers "Mister B. Gone" novel. It is the underworld childhood home of the book's daemon narrator Jakabok Botch. Jakabok fell into a fire as a child and was horribly burned and mutilated which when describing how he now looks is very similar to ghouls.