The sport is Geocaching and is found world wide with over 400,000 cache sites. Basicly a geocacher hides a cache (ammo can etc.) and posts the coordinates on the web site other cachers then enter the coordinates and using a gps finds the cache. The cache stays put and the cacher simply logs in on the cache log book that they have found it. I must say that I'm born and raised in Arizona and have been in the woods most of my life, but geocaching has taken me to places I never knew existed.
Here is the web site: http://www.geocaching.com/