If you make it a puzzle with the clues leading to the Dewey numbers on the spine of the books, or have each stage have the Dewey number for the next stage, then the parking lot can be the GPS coords. This makes it either a puzzle or a multi. I would opt for a puzzle, since if one book disappears, the whole series is not compromised. Sounds like a really fun concept, too bad it is too far away for us to try. Good luck.