From Steve Jackson Games:

Subterranean Secrets!

The hunt for forbidden knowledge goes underground! Explore the Midden of the Mi-Go! Dig yourself out of the Dunwich Ditch! Brave the blue light of K'n-Yan! Maybe all at once . . .

Munchkin Cthulhu has already driven you mad, and now it's even madder! The 16 Portals and 20 Dungeons in Crazed Caverns open up whole new dimensions to explore . . . and we all know what a great idea that can be, right? What could go wrong?

This is an expansion for Munchkin Cthulhu. It is not a stand-alone game.