Geocaching is a well-known outdoor hobby around the world. Participants hide containers called geocaches into nature or the built environment. Inside of these containers are log books and a pen as well as possibly a small trade item.
The location of a cache is indicated on the Internet as coordinates, so seekers of geocaches can look for caches using GPS tracking devices, for instance. However, the coordinates of a geocache are not always given directly, instead you have to also solve a puzzle or perform a task to find the cache.