Geocaching (ˈdʒiːoʊkæʃɪŋ, ) is an outdoor recreational activity, in which participants use a Global Positioning System (GPS) receiver or mobile device and other navigational techniques to hide and seek containers, called "geocaches" or "caches", at specific locations marked by coordinates all over the world. As of 2023, there are over 3 million active caches worldwide.
Geocaching can be considered a location-based game. A typical cache is a small waterproof container containing a logbook and sometimes a pen or pencil. The geocacher signs the log with their established code name/username and dates it, in order to prove that they found the cache. After signing the log, the cache must be placed back exactly where the person found it. Larger containers such as plastic storage containers (Tupperware or similar) or ammo boxes can also contain items for trading, such as toys or trinkets, usually of more sentimental worth than financial. Geocaching shares many aspects with benchmarking, trigpointing, orienteering, treasure hunting, letterboxing, trail blazing, and Munzee.
Geocaching was originally similar to the game letterboxing (which originated in 1854), which uses clues and references to landmarks embedded in stories. Geocaching was conceived shortly after the removal of Selective Availability from the Global Positioning System on May 2, 2000 (Blue Switch Day), because the improved accuracy of the system allowed for a small container to be specifically placed and located.
The first documented placement of a GPS-located cache took place on May 3, 2000, by Dave Ulmer of Beavercreek, Oregon. The location was posted on the Usenet newsgroup sci.geo.satellite-nav at . Within three days, the cache had been found twice, first by Mike Teague. According to Dave Ulmer's message, this cache was a black plastic bucket that was partially buried and contained software, videos, books, money, a can of beans, and a slingshot. The geocache and most of its contents were eventually destroyed by a lawn mower; the can of beans was the only item salvaged and was turned into a trackable item called the "Original Can of Beans".