Geocaching
BLUF: Treasure hunting/hiking with GPS
Basically you go to http://www.geocaching.com/ and sign up and download waypoints into your GPS. Then you go out and find them. Some are thimble size and you only sign the logbog. They can be as big as storage tub full of goodies for you to trade out.
All you need is a GPS. Take the whole family. It gets you outside, it gets you to learn your GPS, it gets you to learn terrain negotiation, some minor mapping. It's healthy, in essence it's free(except the GPS) and you can make a whole day out of it, plan camping trips around it.
Plus if you get good at it you can set up your own caches, which you don't have to do with Geocache and you can put them near points of interest for emergencies, it will also show you places you may not have known about and give you ideas for emeregency situations in the wilderness.
Anyways, it's fun, trust me.