Geocaches, or "caches", are the key playing pieces in the sport of geocaching. As the object of the game is to find these caches, they come in a variety of different shapes and sizes, and may be hidden in obvious to maddeningly obscure locations.
In the most fundamental sense, a geocache will consist of a container placed at a location of interest, the coordinates of which have been posted online, enabling other players to find the same spot using their GPS receivers. What makes a location interesting can vary wildly from cache to cache. At many geocache locations, the surrounding area has some attractive feature, be it a bit of local history or simply a gorgeous view. Sometimes, however, the sole draw to the geocache's hiding place is the fact that there is a geocache there.
Inside a Geocache
Upon finding a geocache, most cachers decide to open it, in order to access the goodies inside. Practically every geocache contains some form of log for successful seekers to sign with their name (or geocaching handle), and the date. Depending on the size of the cache, the log may or may not also have room for additional comments.
While this is not true for smaller caches, many geocaches also contain trade items (or "swag") of various sorts. These items are fair game for anyone who opens the cache to take-- provided, of course, that they leave an item of equal or greater value. A larger list is given in the trade items article, but typical trade items include toys, memorabilia, coupons, and signature items.
Caches may also contain hitch hikers. Hitch hikers are items branded with unique serial numbers, allowing them to be tracked on the Geocaching website. While it's acceptable for cachers to keep the other trade items they find as their own personal belongings, hitch hikers, as their name suggests, are designed to travel from cache to cache. As such, it is expressly against the rules for players to keep hitch hikers that they find as their own.