The Phantom Tollbooth
I was 12, I know this because it says so inside the cover, and I must have read it a million times, I know this because I can still remember the names of the places Milo visits.
The Phantom Tollbooth by Norton Juster
Finally, despite his protestations, I am now reading it to my 10 year old. I am beside myself. The 10 year old isn't beside himself, he's putting up with me because he's kind enough to let me get it out of my system. Every few months I dust it off and waft it about in his general direction, he's done fighting it now, this is something he needs to just push on through.
The best bit so far, for my son, is working out that I first read this book 36 years ago. How freaking hilarious is that? Very, when you're 10. Not at all, when you're 46.