Geocaching is a lot of fun and a good way to sharpen your GPS navigation skills. It's actually modern treasure hunting, except you don't get to keep what you find. With geocaching, you find the "treasure" and replace it with something else. Then you take what you find and place it in another cache. The item is usually some sort of collectible of minor actual value.
The word geocaching is pronounced "geo-cashing." Traditionally by definition, a cache is a place where supplies or food is hidden. The idea of the sport is to have people start caches all around the world and then use the Internet to publish the locations of the caches. A logbook is kept in the cache and the cache should be waterproof. Any time you take and leave something, you're supposed to make a note of it in the logbook.
By entering the waypoints into your GPS receiver, you follow the directions to the cache. It sounds easy, but rarely is. People are very creative in their placement of the cache. Sometimes they're found in urban settings; above ground, below ground, or inside buildings. According to the popular website Geocaching.com, they list over 472,000 active caches worldwide.