http://beyond.divinedivinity.net/help/act4_test3.htm

here is the dungeon with the chest key => number 4 on Hellfighter's map. I think, it was the cave ghost Raanaar.

and the chest is
http://beyond.divinedivinity.net/help/act4_academy_l3.htm

in room number 7, the pool is on 12.
Kiya