Booking Through Thursday

I haven't done this for a while, but the question this week interested me:
What was the most unusual (for you) book you ever read? Either because the book itself was completely from out in left field somewhere, or was a genre you never read, or was the only book available on a long flight… whatever? What (not counting school textbooks, though literature read for classes counts) was furthest outside your usual comfort zone/familiar territory?
And, did you like it? Did it stretch your boundaries? Did you shut it with a shudder the instant you were done? Did it make you think? Have nightmares? Kick off a new obsession?

The most unusual book I have ever read (and I believe I've mentioned it here before) is Pale Fire, by Nabokov. It was part of my Modernist Fiction course in my last year at university and I remember almost none of it. Except that it was painful to read. It's a novel, told in poetry, that's a whodunit. The narrator is untrustworthy at best and, according to our lecturer there was a big payoff at the end. The only payoff I got was from finishing the damn thing!
So. Um. It's Pale Fire. :)