So I just bought the game for xbox 360. Started the first level, killed the bad guys, did as I was told. Managed to find all the relics, killed the big spider thing, then picked up the crystal.

For the last 20-30 minutes I've been doing circles in the room you pick up the crystal trying to work out how to get out.

I've tried jumping from the platform in the middle onto the chains but its not working and can see no other way out.

How do I get out!!!!!?