The final Battle level has tons of stone and lava in it - very dark. This is a great place to have the thunder hammer. There are many crates and levels, and you have to be careful to take out the enemies when you can. If you wade down into them, they chew away at your energy amazingly fast! Stop at every edge and kill off any enemies you can reach with your weapons, before moving forward.

The final runestone is of course in this level. When you get it, you can face the final battle by walking into the runestone circle.

Gauntlet Legends Walkthrough