I know all about Geocaching as my brother and his kids are really into it. They use a hand held GPS and the infomation from the Geocaching web site to find caches (boxes) wtih either notebooks for signing in, travelling items to be left at another cache, or little goodies to take and leave something in their place. It's a really fun hobby!
I have now heard a a similar outdoor treasure hunt called "Letterboxing." Letterboxing uses clues and compasses rather than GPS, it seems, and centers around the boxes containing a small logbook where you add your own personal stamp when you find the letterbox.
Great fun!
