Geocaching is fun.
It combines the fun of hiking and exploring with friends, (often to places you would not otherwise go to), with playing with cool high-tech gadgets and finding "treasures" along the way.
It is easy and relatively inexpensive to do.
All you need is a GPS receiver (from under $100 to about $500 - your cell phone might even have an optional application that does the same thing), a computer, and a good pair of walking shoes.
It is a hobby that the entire family can do together. It can be as easy as walking around your own neighborhood, or as hard as a wilderness expedition - it's up to you.
Basically:
You go to a web site (like geocache.com) and find coordinates for some caches that people have left (on public land) for others to find. A "cache" may be as small as a film canister or as large as a cookie tin or ammo box. Inside the cache people leave trinkets and a notepad.
Then you head out (with your GPS) and see if you can find the cache. The fun part is hiking and looking around. Even with the coordinates, you have to use some detective skills to find where it is hidden. Some are easy to find (like those I'm finding in the photos) and others are deviously difficult!
When you find the cache - sign the notebook inside, take a trinket and leave one of your own. Then put everything back like it was for the next person and go look for another one.
Be sure to pick a hike that is at the level you are prepared for. Caches are graded on the web site and can be very easy or very demanding. The Boy Scouts are right - be prepared. (Always carry extra batteries for your GPS.) Think about what kind of country you are heading into and who you are taking with you.
Where I live being prepared, at minimum, means wearing good boots, bringing LOTS of water, wearing a hat and watching out for scorpions and snakes under or around where you walk, sit or put your hands!
If you do see them out in the wilderness - just leave them alone. You're in their world.