Wikipedia
Geohashing is an outdoor recreational activity inspired by the xkcd webcomic, in which participants have to reach a random location (chosen by a computer algorithm), prove their achievement by taking a picture of a Global Positioning System (GPS) receiver or another mobile device and then tell the story of their trip online. Proof based on non-electronic navigation is also acceptable.
Whereas other outdoor recreational activities like geocaching have a precise goal, geohashing is mainly fueled by its pointlessness, which is deemed amusing by its players. (However, a variation on geocaching, known as geodashing, features a closely comparable principle.) The resulting geohashing community and culture is thus extremely tongue-in-cheek, supporting any kind of humorous behavior during the practice of geohashing and resulting in a parody of traditional outdoor activities. Navigating to a random point need not be pointless. Some geohashers document new mapping features they find on the OpenStreetMap project.