[Kaleban]

Check the corpse of the beholder (hold down Tab to highlight treasure piles) and you should be able to click on a "treasure" which is actually the eye of the beholder.

So much for beauty eh?
WAH HA HA HA!!

Seriously though, put it in the cauldron and then click on the machine, and you should be transported out. Don't forget to pick up the Staff of the Magi from the dead female wizard...