The inevitable successor to the compass-based navigation/hunts of orienteering, geocaching relies on GPS readngs. A geocache is a item of some sort, usually a container filled with "treasure", which is secreted in some public location and pinpointed by GPS. The geocache's location is then described on a geocaching website. Geocaching is one of the fastest growing ad-hoc communities.
Popular items for geocaches include other ad-hoc community items, such as Where's George-marked currency.