In Subrosia. First, in Holodrum, go far north to the remains of the temple of Seasons. there is an entrance to Subrosia there. Then, in Sub., find a cave with a Subrosian throwing stuff in lava. Figure out this puzzle (it's easy, but I'll let you do it), then go back to Holodrum, temple remains. This should lead you to another entrance to Subrosia (top left corner), where the eighth level rests.
If this is not correct, or helpful enough, search for a walkthrough on the net. I'm trying to recall how I did it last month and it's 2 in the morning right now, so I might not be remembering it just right. Anway, try it!
