What: The use of GPS receivers to seek containers called geocaches in a multitude of outdoor locations. When geocachers find a cache, they sign a logbook which certifies their find, then virtually log the find on geocaching.com. The cachers often will take an item or leave an item, many of them trackable online.

Why: Born of a Luddite activity called letterboxing, geocaching came to life when President Clinton removed a Cold War-remnant series of errors called selective availability from the Global Positioning System on May 1, 2000. Two days later, Dave Ulmer dropped a bucket in The Middle of Nowhere, Oregon. Some other fellow found it, and the virus began to spread. The activity unites three disparate key elements: First, you go somewhere you haven’t been before. Second, you leave something in the cache, and take something you find. Third, you tell everyone you’ve been there by logging your find. If you’re an explorer, a collector, or an egotist—and I know you’re at least one of those—geocaching will appeal to you. Or perhaps if you’re an absurdist: After all, you’re using billion-dollar satellites to find tupperware.

Impact: In less than a decade, geocachers have placed almost 900,000 active caches. Wherever you are (assuming you are not reading this in the ocean or on the moon), there are some near you right now. You can find a bunch by turning on your iPhone, downloading the Geocaching app, and hitting “Find Nearby Caches.” That won’t satisfy you, though, because an iPhone is a poor GPS unit. You will soon want a handheld GPSr. You will want to leave your house every weekend. You will want to try harder caches. You will want to leave your mark on the world. You will want to enjoy life.

Personal Connection: Three hundred and fifty caches later, Evon and I are serious cachers. Geocaching has acquainted us with hundreds of places we would never have seen. We own a Garmin 60CSX, a very good receiver, plus two other Garmins as backup. We have wandered dark mountain shafts, crawled up 400-foot drainpipes, and hung off cliff faces. And we have placed one of our own, just near our house. So here’s our offer to you: Come by, and we’ll hand you a GPSr. You can find our cache, and sign the log. Whatever happens after that is up to you.

Other Contenders: Lindy bombing, the art of swing-dancing on things not typically swing-danced upon, here demonstrated by Seattleites Celeste and Lukas; birdwatching, especially if you can hang out with David Attenborough; playing a handheld video game in wardriving mode, seeking WiFi hotspots to unlock treasures, allies, and adventures; road rallying, driving a car from checkpoint to checkpoint—or, if you’re puzzlingly inclined, playing The Game.