Book Crossing.

Imagine a travelling gnome.

You see it in Madrid.
Someone pick it up and travels to Brazil for spring break.

Then the person left the gnome again, this time by a blind musician in a park. And it continues to travel, as people like you and me find him.

Someone exchange the idea of the gnome with books.
Leave a book on a bench.
See where it ends up.

www.bookcrossing.com