I think Geocaching might be something that I could really get into.

Basically, you look up on this website the latitude and longitude of a stash of stuff that someone's already placed (a "cache"), then you go out there with your GPS unit, find the spot (within 20 feet or so), then try to find the cache. If you find it, there's something inside left by the last person. You can take the contents of the cache and leave something of your own for the next person, or you can just look at it. There's also a logbook listing the people who've found the cache before you.

It's like a combination of hiking, a treasure hunt, and a spy movie. I think I'll have to buy a cheap GPS unit and give it a try.