A few months ago, I started geocaching
. It's a sort of game, not unlike a treasure hunt. One person will hide a container (often full of trinkets) somewhere in the world, then post the geographic coordinates of its location to the Internet. People with GPS receivers are encouraged to seek out the containers, log their visits, and trade trinkets if they wish.
Last week, I hid one myself for the first time. But instead of putting up the actual coordinates, I concealed them within a puzzle. Since the puzzle might still be of interest to people who aren't close enough to visit the actual cache, I thought I'd put a link to it