The exit to the lower level is the very bottom most walkway that you can see in The great hall that holds all the mana beams. It is accessed via a long tunnel that is the last doorway you encounter if you follow the pathway all the way around the room you first enter which is called Nalonwyn Great Hall. (Tangent sub-quest. Find the body of Taylin who was thrown to his death by Rindsey by exploring this tunnels other exit which exits into Tamriel near the base of the cliff beneath the students quarters. Follow the path till you find Taylin.)
I walked out the door and followed the path as far as I could and i didn't see any dead body outside. Can somebody who has found him before help me out with a screen shot or something?