This is interesting. Can those that have played it give us all a run down on what is involved? What is the point and what are the rules? I went to the website but, it appears that you have to sign up in order to get the details.
There are no "rules" other than respect for peoples property. For example, I have heard that caches are hidden on peoples property. That indicates that you are welcome to come onto the property but I was never comfortable doing that so I wouldn't ... unless it was something like a big open field and the cache was near the road. The object is simply to get out and enjoy the outdoors.
How it works is easy. Someone hides a cache, usually a weather proof plastic box. Typically the caches are in a public place, like a park. The person hiding the cache makes note of it's GPS coordinates and enters them into a website. There are many websites that cater to geocachers. If you discover that you enjoy it, you could make up one and hide it and see how many people stop by to find it.
After the GPS coordinates are available, people make note of the coordinates then they try to find the cache. Some are easy to find, others are harder. They could be inside a dead tree, inside a hedge, under a bench etc. They are rarely in plain site, though some are visible if you just look around a bit since you know where to look.
Once you find the caches you typically sign a log, so the person hiding the cache knows how many people have found the cache. Sometimes the hider of the cache will put "treasures" in the cache. If you find the cache you are allowed to take a "treasure" but you are supposed to put something back of equal value. A very popular "treasure" is AA batteries ... and that is what I always put in if I take something.
After you sign the log and take a "treasure" you put the cache back where you found it. Places like a park may have several caches hidden in them, so you could go on and try to find the next one if you choose.
That's it. Everything works on the honor system and it is just for fun. I did it with my kids for a while ... there are a couple caches hidden in the park that is with-in walking distance, but they got bored with it pretty quickly. If you like to get out and enjoy the outdoors you would probably like geocaching.
Copper