Geocaching is a scavenger hunt-like hobby that takes people to all sorts of interesting locations hunting for treasures (called caches). After hiding the cache, the hider records the longitude and latitude of the location for seekers to use. Seekers use GPS devices to get them as close as possible to the cache and then hunt for it.
Once you find the cache, you sign the logbook contained inside. You might find some cool swag to take with you, too!
The official geocaching site is www.geocaching.com. It's free for anyone to join and to hunt caches all over the world. When you find a cache, you can log on to geocaching.com and leave a message in the online logbook for each cache, too, or share pictures of your adventure searching for the cache. The library's geocaching profile (including all of our hides) can be found here.
Need more info?
Read the official geocaching.com guide.