In addition to the goodies, caches nearly always contain a log book of some sort so that you can record your thoughts and scribble a note for future cache visitors.

Sounds fun. So what's a GPS receiver?
GPS stands for "Global Positioning System," a series of two dozen satellites in low Earth orbit that continuously broadcast their position. GPS receivers are able to triangulate on these signals and determine your location on the Earth's surface. Once you select a cache and enter its coordinates into the GPS receiver, the receiver can tell you how far away the cache is and in what direction it lies.

For more information, How Stuff Works has a good article called "How GPS Receivers Work" that you might find of interest.

That sounds easy. What's the catch?
The catch is, that getting there is half the fun. Knowing that a cache is, for example, 11.2 miles northwest of you doesn't do you much good if there's an impassible mountain range, a lake, or something else in your way. You need to find your way around. Of course, if you brought a kayak with you, a lake might not be a barrier.

When hunting for my second cache, I was able to drive to within a quarter mile of the cache's location, but the only way to it led through some private property. (Crossing private property without the owner's permission is a big geocaching no-no!) So I had to drive around and find another way to get to the cache. After some searching, I found a local park I hadn't known about before. I soon found the right trailhead and a path that led to within 20 feet of the cache.

So what does one find in a typical cache?
You could find almost anything in a cache, depending on its size. Small toys, books, LEGO bricks or mini-figs, stuffed animals, music CDs, CD-ROMS, tapes, non-perishable food items, and the log of course.

Some caches contain a disposable camera. The camera isn't a goodie to be taken though; just take a picture of yourself and tell the cache owner if you snap the last photo. The cache owner can then recover the camera, develop the film, and put your smiling mug on their web page along with all the other visitors to the cache.

The smallest caches, known are microcaches, typically just have a stub of pencil and a few slips of paper to serve as a log--it's rare for these caches to have any goodies.

How much does geocaching cost?
Geocaching itself is completely free. Well, you will need a GPS receiver and those start out at about US$100 (and can go quite a bit higher), but besides that it's free. When you go out on a hunt though you should always bring a little extra money with you in case you need to pay a parking fee, buy some gas, get pizza on the way back...you get the idea.

What should I NOT put in a cache?
Whole families go geocaching together so items should be safe and legal for all. No alcohol, drugs, explosives, Menudo tapes, etc. Use common sense!

Who goes geocaching?
Anybody and everybody who enjoys the outdoors and looking for treasure goes geocaching! I've met families with their kids, people looking for something to do while walking their dog, and solo geocachers of a variety of ages.

Most cache listings do have some sort of difficulty rating associated with them so if you're bringing small children or your grandmother with you, you might want to pick an easier cache that's no more than a quarter mile walk in the park. On the other hand, if your grandmother is a divemaster that has logged over thousand dives, you and she should grab your SCUBA gear and try your luck finding that cache I heard about on the bottom of the Red Sea!

What precautions should I take?
Take the same precautions you'd use if you were going on a hike. Tell someone where you're going and when you expect to return. Bring maps, water, sunscreen, and maybe a cell phone if you have one. Watch out for poison oak, ticks, snakes, cougars, and convicts who just broke out of the maximum security prison down the road. Above all else, bring your common sense with you!

Who invented geocaching?
The first cache was placed by Dave Ulmer near Portland, Oregon on May 3rd, 2000. Three days later, two people who had read about the cache on the sci.geo.satellite-nav newsgroup found the cache and entered their names in its log: geocaching was born!