Emily Mellgren, a schoolteacher from Maryland, began geocaching in 2005. Her children were small back then, and she figured it would be a good way to get them outdoors.
Geocaching is a recreational activity where one is given online coordinates to find capsules or containers that are registered on the geocaching website, some of which contain items left by other geocachers, or stamps, or simply a piece of paper to sign. There is now an official geocaching smartphone application. One can pull up a map, zoom in on their location and see locations of every geocache around them. Key Largo alone has dozens of them.