Letterboxing is another form of treasure hunting that uses clues instead of coordinates. In some cases, the letterbox owner has made their container both a letterbox and a geocache and posted its coordinates on Geocaching.com. These types of geocaches will contain a stamp that is meant to remain in the box and is used by letterboxers to record their visit. To read more about letterboxing, visit Letterboxing North America.
Individual letterboxes contain a notebook and a rubber stamp, preferably hand carved or custom made. Finders make an imprint of the letterbox's stamp in their personal notebook, and leave an impression of their personal signature stamp on the letterbox's "visitors' book" or "logbook" — as proof of having found the box and letting other letterboxers know who has visited.
The origin of letterboxing can be traced to Dartmoor, Devon, England in 1854. Interest in letterboxing in the U.S. is generally considered to have started with a feature article in the Smithsonian Magazine in April 1998. The growing popularity of the somewhat similar activity of geocaching during the 2000s has increased interest in letterboxing as well. Clues to American letterboxes are commonly published on several different websites.