Just googled a solution.
The area before the bridge is a small spiral stair case. There is a secret wall inside that room that takes you to the Darkmoon priest ring. Find this room. There should be a couple archers and normal skeletons. Run on thru and you will get ambushed by a giant skeleton. I think you can run by him(get the ring while you are there), take a right, go up the ramp, and go kill the pyro mage.
From the spot where you kill the mage, there is an opening in the wall and a ladder. The ladder should be on the right i believe Take the ladder. Continue through this path you will get to the end when you find a spell and next to that is a drop point. This is the floor you need to fall down. You will now be in the room leading to the first flipped bridge and can backtrack out of the place.
Try this.
