Geocaching is a modern-day take on the scavenger hunt: Participants use superaccurate GPS positioning to locate hidden treasures, or caches. The caches, which can be well concealed, usually contain small trinkets and a log book in which you can record that you found the cache before you put it back for the next person to find.
As of August 2008, Geocaching.com, a central site for the hobby, had almost 650,000 caches marked. Once you've registered for a free account with the site, you can download a Google Earth network link to see all of the different types of caches near a location. If you're lucky, one of your local caches may also contain a "Travel Bug," which you are encouraged to move physically to a cache in a new location. A unique code that you enter along with the cache's coordinates at the Web site then allows fellow geocachers to track the bug as it travels around the globe.