Geocaching is an outdoor activity where participants use GPS devices to hide and seek containers called geocaches around the world. A typical geocache is a small waterproof container containing a logbook. To play, geocachers obtain GPS coordinates for a hidden cache, locate it using a GPS receiver, record their visit in the logbook, and may leave a small trinket to trade for another geocache's contents. With over 600,000 geocaches hidden worldwide as of 2008, it is a popular hobby that gets families outdoors to explore new areas.