Fallout 3 locations project
Underworld Outfitters is a shop, run by the ghoul Tulip. It can be found on the left hand side of the ground floor of Underworld (when the player has their back turned to the main entrance), and contains a variety of items. There is a 10mm pistol, an abundance of normal and bent tin cans, a safe, a computer, and other items. If the fire extinguisher is shot, when you return, the pieces will be put back together. Its name could be a reference to the real life clothing store "Urban Outfitters".
Her store has a variety of armor and ammo, and she also has a surprising amount of money(anywhere from 400 to 600 caps) making her a great shop for mid level characters.
One of the 3 Schematics - Railway Rifle can be purchased here.