In the spring of 2000, a man in Oregon hid a box of toys in the woods, posted the geographic coordinates of its location on a Web site, and issued a challenge for others to find it. People used their GPS receivers to find his treasure, and a new game was born. Today over a million people worldwide participate in geocaching, hiding stashes of trinkets in a variety of locations--from a grove of trees to a cliff ledge to the depths of a riverbed--and...