Geocaching is an activity which combines a love of the outdoors with the use of highly sophisticated modern technology. Basically geocaching is like a traditional treasure hunt, but instead of having a paper map with an X marking the spot, "cachers" use a handheld portable device, around the size of a mobile phone, called a Global Positioning System receiver (or GPS as its more commonly known) to locate their position on the earth's surface.

Using a system of dedicated satellites, a GPS can accurately and rapidly give a user their coordinates. If a user knows the coordinates of a particular thing on the earth's surface the GPS can guide the user to this item, showing the user's distance and direction from the item. Geocaching uses this functionality to enable cachers to place some treasure (a cache) at a particular location and then share the coordinates with the rest of the geocaching community (through the official geocaching webpage ). Other cachers can then programme these coordinates into their GPS and go hunting! When they find the cache they can log their visit in the logbook and exchange an item in the cache for an item they have brought. 

So where did it all start.....well where everything does, on the internet! On May 1st, 2000,  the GPS signal degradation called "Select Availabilty" (SA) was removed by the Clinton Administration. Two days later, on May 3rd 2000 a guy called Dave Ulmer hid the first geocach0nd, Oregon, USA, and then posted about it on the sci.geo.satellite-nav newsgroup: