The Underworld Tavern is a bar in Hell's Kitchen, New York City in 2052. It is located beside the barricaded overpass leading to the NSF Headquarters, with a back exit leading to the 'Ton Hotel fire escape and the Free Clinic.
The bartender is Jordan Shea, a former mechanically augmented agent of UNATCO. It is never explained why she left the service, but she shows contempt for JC when he mentions that he works for UNATCO. One of JoJo Fine's cronies sells his wares in the tavern, notably Ambrosia.
Jock and Janey can be found here during JC's first visit in the area. Upon returning from Hong Kong, there will be a marine named Vinny in the same area as Jock earlier. A dialogue option with Vinny will cause the first pair of guards at the Brooklyn Naval Shipyard to let the player through the first gate, eliminating the need to break in or sneak through the hazardous tunnels below.