Methinks that you basically buy a GPS system (handheld or add on for phone/pda etc) download the coordinates for a Cache, then set off and walk to try and find it.
The cache contains goodies (sometimes) which you can swap for something you took along, a log book to note what went in and out and who found it etc.
Then on your return you log your find on the cache's webpage.
Sometimes if the environment doesn't lend itself to hiding a cache (typically a waterproof lunchbox or similar) the cache is simething you have to see to prove you got there OK.
I enjoy walking, and am always interested in new ways to persuade me to get out and see the countryside - is this a good way? Are there any other excursions that can be reccomended?
We do it-- my wife was attracted to it and quite often spends time checking out what caches there are in places we might be going to. The main site we use is http://www.geocaching.com/ and we have found that geocachers quite often manage to find interesting places we never knew existed, so it's not just a way to waste a few hours!
We're not as fanatical as some get (one or two people have notched up nearly as many caches as Peter Vaughan has made posts! :shock: -- and its still a young activity/sport) At the last count we had found 27 caches since we started just before Christmas
I'm involved mainly because my Treo 650 and bluetooth GPS got roped in with some software that cost about $10 and I must admit that some of the cryptic clues that people dream up are interesting as well as caches being placed in interesting locations