Getting recognitition for the completion of this quest is hard. Sometimes we simply do too much.
This is what Kingkongcobra has to say on the topic:

"Enter from top. Run to door. Break board. Exit. That's all!! But don't save or reload or rest or heal or regenerate. Quest completed and leaves questbook, 20,000 XP reward."

You also shouldn't use Lloyd's Beacon or Town Portal.
In addition to the XP you get +5 to might and magic for all characters (thanks Aces).

The hall respawns when you leave so you can return and get the experience points from killing the foes at your leisure.