Spoilers . . . . . . . . . A hidden switch along one of the walls in library leads to an exit. However, it is guarded with some difficult monsters. You may want to wait a bit, probably level 12 or so. Also, if you go to www.spidweb.com, the forums there will have a lot more information. They are frequented more than this one.
Only the intelligent can recognize their own ignorance.