Geocaching is a recreational activity which works similar to an old fashioned treasure hunt.

People hide caches or treasure boxes, record the GPS coordinates of the box and then publish the details on the website geocaching.com.

Anyone with a GPS receiver can get the location of these hidden caches and then spend a fun filled afternoon using their handset or phone to track down the box with the aid of clues or photos.

To get started geocaching visit the website and set up an account to record your hunts and communicate with other users around the world.

GPS - the Global Positioning System - was invented by the United States military as a way to accurately navigate and fight battles.

It was later decided to open up the network of 24 satellites to all civilian users as a valuable navigation tool for aircraft, ships and hikers amongst other users.

Wikipedia describes the system as providing:

reliable location and time information in all weather and at all times and anywhere on or near the Earth when and where there is an unobstructed line of sight to four or more GPS satellites

Read more about the history and amazing technology behind GPS at http://en.wikipedia.org/wiki/Global_Positioning_System