The Ruins by Scott Smith
The beginning of this novel is a lot like the show "Lost." Four young Americans and a Greek and a German friend are taking a little hike into the Mexican jungle. They are looking for the German's brother, who ran off chasing after a hot archeologist chick. As soon as they enter the jungle, weird stuff starts to happen.
But then, somewhere in the 100-page vicinity, you start to figure out what is really going on. And from then on out, this book is pure horror. Stephen King territory. And it was psychologically freakin' harrowing. I had a hard time finishing the book. It's difficult to imagine something so implausible could be so scary, but this book scared the hell out of me. At times it made my physically nauseous. Does that make it a good book? I have no idea. Read at your own risk - not for the faint of heart.