All you need is a GPS receiver and a sense of adventure. You can easily spend the entire day on the hunt. My wife and I pick out parks we want to go to, plot out on the caches in the park and off we go. You see some amazing sites along the way, the caching serves as a purpose, next thing you know you have walked 10 miles and haven't spent the day with your backside sticking out of the refrigerator.
Hey - now there's a fun idea... Pinging my brother and husband too! Geocaching FAQ - Frequently Asked Questions About Geocaching. We have a GPS device we're just learning to use, and I'm amazed at the number of caches nearby here. I've got some ideas on where we could plant some too :~D
That sounds fun!