People can develop self-enclosed story files (called "cartridges") that are installed on a GPS enabled unit along with a player program. The player and story take advantage of the location information provided by the GPS to trigger in-game events, such as reaching a virtual object or interacting with characters. Completing an adventure can require reaching different locations and solving puzzles.
Cartridges are coded in Lua. Lua may be used directly, but a builder is usually used.
The Wherigo site offers a builder application and a database of adventures free for download, though the builder has remained in its Alpha version since its last release in May, 2008. The official player is only available for Pocket PC. A built-in player is available on Garmin Colorado and Oregon GPS models.