Books that will blow my mind....?

I don't want a cute teen story or a vampire/werewolf anything. I'm looking for some books that will blow my mind, like literary treasure. Cult classics are a good place to begin, I don't really want anything too "mainstream classic" like Huckleberry Finn or secret garden. It can be fiction or nonfiction. Something out of the ordinary, possibly involving abstract concepts. Thank you! :D p.s I already know hitchhikers guide to the galaxy :P