Today, I went geocaching for the first time ever. This is loads and loads of fun. My wife showed me the website a few days ago. I borrowed a friend's GPS unit for the weekend and we went out today and had a blast. Go to the website for all the details, but here's the basic gist: someone fills a small container up with various trinkets and stuff and hides it, usually a little bit off a trail in a park or something. Then they post the exact coordinates on the website and anyone can find out where the cache is. Once you get the coordinates, you program them into your GPS unit and go look for it. It's not always easy (although the three we found today were pretty easy), even with the exact coordinates. So, from about 2pm to 6pm, we checked out three nice hiking areas within a few miles of our house -- two of which I didn't even know were there! We ended up finding Hawk 4, Hawk 5, and Hawk 8.
This is loads and loads of fun. If you've got a GPS, go look for a nearby cache now. If you don't have a GPS, go get one so you can start looking. I don't look forward to having to return my borrowed one.