The game basically involves a GPS user hiding "treasure" (this container and its contents), and publishing the exact coordinates so other GPS users can come on a "treasure hunt" to find it. The only rules are: if you take something from the cache, you must leave something for the cache, and you must write about your visit in the logbook.
Geocaching is open to everyone with a GPS and a sense of adventure. There are similar sites all over the world.
To consult the contents of this page, open the version in French.