The descent
(Book)

A mountaineer in Tibet falls down a hole to emerge in a subterranean world, populated by brutish and horned creatures. Is this the hell of the Bible? As scientists and philosophers debate, a global race gets underway to exploit its fabulous mineral deposits.

We are not alone...In a cave in the Himalayas, a guide discovers a self-mutilated body with the warning--Satan exists. In the Kalahari Desert, a nun unearths evidence of a proto-human species and a deity called Older-than-Old. In Bosnia, something has been feeding upon the dead in a mass grave. So begins mankind's most shocking realization: that the underworld is a vast geological labyrinth populated by another race of beings. Some call them devils or demons. But they are real. They are down there. And they are waiting for us to find them... -- from Amazon.