In the game Dragon Age Origins, how do you get out of the elven burial chamber?

I'm in the lower ruins and somehow I got into this elven burial chamber, idk how, and there is only one way out. A door, which is locked. I can't find the key anywhere and I'm stuck in here. How do I get out?In the game Dragon Age Origins, how do you get out of the elven burial chamber?
Did you defeat the enemies up on the upper level with the coffin with the piece of the juggernaut armor in it?



If so, then you might be having a glitch.