If you can remember the bridge you tried to cross went down.What you need to do after you killed the four demons at the first mouth is finding the room with the switch wich puts the bridge back up.After you crossed the bridge you find Voratus chamber.After defeating him or winning his deal you can go to the second mouth and choose your reward.
Right(demon steel) you find 2 chest's and a great sacrophag with a blade of death and many other powerful armor pieces.
Left:2 chest's and I think this is the only place in the game where you can find the cataclysm spell.(It's worth the trouble)!
