Burnmaster (Fallout 3)

Go to the Falls Church/Mason District Metro Station (the one with the ghouls that connects Falls Church and the Hubris comics area). Don't go up the stairs to the second level like you would to get to hubris comics, but stay down and go into the train tunnels. It will curve around past a couple of glowing ones and there will be an entrance to a utility tunnel. Go in there. Follow that until you get to where the tunnel goes down into the water. Go into the water and then make a left through a broken passage in the tunnel. Swim for a bit until you find a ramp that goes up. At the top of the ramp if you turn around there will be the burnmaster.