Scariest book you've ever read?

Edgar Allen Poe wrote short stories rather than the novels you have previously been reading. However, he wrote two that I can still remember from high school because of how creepy/weird they were. The books are "The Pit and the Pendulum" and "The Telltale Heart"'. Both were made into movies when Vincent Price was considered the best psychotic villain ever. The latter book was especially creepy.