Geocaching is an outdoor treasure-hunting game in which the participants use a Global Positioning System (GPS) receiver or other navigational techniques to hide and seek containers (called "geocaches" or "caches") anywhere in the world. A typical cache is a small waterproof container containing a logbook and "treasure," usually toys or trinkets of little value. Today, well over 800,000 geocaches are registered on various websites devoted to the pastime. Geocaches are currently placed in over 100 countries around the world and on all seven continents, including Antarctica. - WikiPedia
Downloaded Geopher lite to my iPhone, WOW what a kick! Before you buy, read the Geopher blog regarding the future of this iPhone Geocache Application
Geocaching from your iPhone is going to go viral. With the rise in GPS embeded in our handhelds even your Mom will want to find the Geocache nearby.