Ok, I accepted the sacred oath and picked up the ring under the rotten corpse, what else is left to do? Nivius told me to seek the second watcher but how do i leave the Crypt? *** Post Spoiler if Necessary *** TKS

I'm not sure if this is what you wanted to know but here it goes...
Remember the place you picked up that gold key?..Swim there and pull the lever on your left...Go back to the hall beneath the broken staircase and use the elevator roof to get back to the statue..Leave the crypt..
I hope this answers your question...Have fun and good luck...