I can't remember the last time I read a book that actually scared me. What do you fear? Drowning? Tight spaces? The dark? Ghosts? Monsters? It's all here and it's all tangled up in a way that makes you doubt everything you see, amplifying the terror like cavern walls echo voices. This book is grueling in the best way. The characters endure so much, that by the end you are just as exhausted as they are. An incredible, creepy, read.