You are guilt-tripping me for using my copy of Godel, Escher, Bach to raise my monitor before I got around to reading it.
I read it when I was about 9 or 10, I didn't understand any of it at all but I used to pick it up and look at the pictures of the Escher drawings, which were amazing.
Then, after I graduated from college, a friend of mine who was finishing his physics degree mentioned that he had just finished it and that it was life-changing. I read it again and deeply regretted having put it down for those 12 intervening years.
It's a book that works on many levels.