Geocaching is a treasure hunt game done with a handheld GPS unit. The link Sheri posted above will show you where caches are located in your area. Then you get a handheld GPS and hunt them down. When you find them you usually sign the log and exchange trinkets with one found in the cache. Sounds simple, but it's really lots of fun. It has helped us discover a lot of hikes, parks, bicycling opportunities we didn't know about. And they're all over the country, so you can do them on the road too. It's a great excuse to get out and explore.