"After learning of a centuries-old manuscript that contains the passage to the center of the Earth, caving expert Mike Monroe risks it all to follow the path. But what he finds there will alter everything he knows about the world…" I’m guessing author Grieg paid little to no attention in his Earth sciences classes.
The only thing at the center of the Earth is a giant ball of searing hot iron, surrounded by molten iron, surround by molten rock, surrounded by hotter-than-hell rock. If the blurb had described this novel as a scorching read it would have been more accurate, but just as boring a prospect.