From the https://geohashing.site/ homepage:
Geohashing is an adventure, comprising journeys to random places within a given area. Every day, effectively random locations are generated by an algorithm that achieves randomness using stock market data.
Geohashing can easily be combined with mapping.
More information and tools:
- Coordinate calculator: http://geohashing.info (see also https://geohashing.info/wiki)
- Small Hash Inquiry Tool: http://tjum.anthill.de/geohash.html
- Geohashing Poster Tool: https://geohashing.site/geohashing/user:Crox/Poster
- OpenStreetMap Achievement for Geohashers: https://geohashing.site/geohashing/OpenStreetMap_achievement#Background (encourages editing and tracklog uploading)
See also geocaching, another geogame.