[Blocked Image: http://www.larasmansion.com/help/aod/hall08.jpg]
You are saying you are on the ledge shown here?
Did you get the power up?
Then you have to climb back and towards the dome. (a bit to the left .what would be on the right in the picture.)
Lara will turn around at the gap so she's able to climb up. Climb up into the opening quickly and make a backflip to reach the chamber