The House on the Borderland -- William Hope Hodgson
This is the time of year when people like to list the books that scared them or that gave them nightmares. Two of the scariest books I've ever read are about houses: this one and Shirley Jacksons's The Haunting of Hill House. While Jackson's book has plenty of frights and chills, Hodgson's is the one that gave me nightmares. I think it was the swine people, or maybe the journey to the end of the universe. Whatever it was, it haunted me for a few nights after I read it. I can't think of any other book that's affected me that way.