The Underdwelling
It's Boyd's first day on the lower levels of the mines. When his coworker Maki falls down a hole, Boyd and a few others go after him and find an ancient cavern that's been sealed up for millions of years. After a bit of exploring, they get trapped and find out they are not alone. After a couple of hundred million years, something is very excited to have company...This book creeped me out! It started out innocently but the suspense and horror built quickly and I was unable to put it down until the fantastic ending.