You start at one end of the hallway. The boss is all the way at the opposite end. I think that's the one where a map glitch puts the boss off the map entirely.
I just did this the other night. If I am remembering correctly, the Chamber of the Charmed is supposed to be on the lower level, right? I think that's what the quest says. I did several things that night.
So you go down the ramp to where the rubble blocking a passageway is, and you'll get the message that since it's blocked, you have to speak to someone else. Eventually you get very specific directions of how to get to the chamber. You can then get through a door that wasn't lit/open before, and make your way to the Chamber (which, as stated above, is at the other end of the hallways after going through the newly available door.)
