Nagafen's Lair  

To get to Nagafen's Lair you have to go though and do the "The Oratorium of Thyr "
quest first. To get access to this you have to go up to the 6th level once you complete
this quest there will be a door behind him which will let you move on to Nagafen's Lair.

http://eq2.zam.com/wiki/eq2_zone:The_Oratorium_of_Thyr