With its roots in Dartmoor in England, Letterboxing involves a waterproof box hidden in a scenic location and containing a rubber stamp and notebook; a person uses a series of clues (some are more cryptic than others) and possibly a compass and map to search for a box. Once found, the finder will stamp the box's notebook with his or her personal stamp, and use the box's stamp to mark their own personal notebook. Letterboxers collect the stamps from boxes all over the world. Similar in some ways to geocaching.
"I just got a patch for collecting my first hundred letterboxes!"