N 40° 44.185 W 073° 59.427: the northwest corner of Union Square in New York City. According to information on my phone, “pvdjr” had placed a tiny magnetic canister, no larger than a Civil War shot, somewhere at those coordinates in August, 2011. Since then, it had been found, and replaced, 786 times. It had also not been found—by millions of people who had walked by the well-trafficked spot in the last few years, perhaps shopping at the pleasant Greenmarket in season, or racing to a nearby subway entrance, or crossing the Frederick Law Olmsted–designed park to an office or lunch. That’s because, if they weren’t looking for what pvdjr had hidden, they couldn’t have known it was there.

I don’t know pvdjr, but on a recent winter’s day, I went looking for his handiwork, playing the anonymous game of hide-and-seek known as geocaching, shared by some 6 million hobbyists and enthusiasts around the world. The game is simple: individual geocachers hide containers—there are more than 2.3 million active caches—name their treasure, and post coordinates and clues on a Web site (the largest is geocaching.com), so that the caches can be found. Following my phone’s built-in GPS, I knew this cache was somewhere near a corner of the renovated playground. New Yorkers tend not to judge public behavior, but clinging to a sense of dignity, I poked around the bamboo stand there in as nonchalant a manner as I could. This uncovered only a flattened McDonalds coffee cup, some old brown snow, and a dead mouse. Then I ran my hand along railings, feeling for unusual or loose items. Nothing. A light frustration set in. I stepped back and scanned the scene, just another guy in Union Square. The iron fence made a corner, where a green sign was attached: “Park closed Midnight to 6 am.” Where was it?

I play the game occasionally, because it makes me stop and look at places I would normally relegate to the blur of background scenery. It redraws my maps, makes landmarks of standpipes, nooks, cracks, crannies, ledges, bollards, bushes, grates, fences, poles, and sundry urban flotsam. It takes me to places I wouldn’t normally go and uncovers layers under what I thought was familiar. Caches are secret little Pynchonesque way stations; non-players are referred to as “Muggles,” the term in the Harry Potter series for characters unfamiliar with the magical world that exists beside their conventional one.

I was introduced to geocaching by my childhood friend George Z., a lapsed U.S. Geological Survey hydrologist and stay-at-home dad of three in Northern Virginia, who spends many a weekend in the woods caching with his kids and dogs, or alone. Some cachers are quasi-pro. “Starless,” according to his online profile, has made 11,152 finds in at least 54 countries, including one at 10,633 feet elevation near Laguna Morado in Chile, and another at 13 feet below sea level at the Statue of Mohandas Gandhi in San Francisco. Starless is hardly the most prolific hunter out there: eleven obsessives have more than 50,000 finds each.

The game redraws my maps, makes landmarks of standpipes, ledges, bollards, and bushes.

The roots of geocaching are in the Enlightenment ideal of the observable natural world and the Romantic sense of travel for the sake of curiosity and learning. The Victorians played a version of orienteering that involved rambling and stamping passports in the southeastern region of Dartmoor, still home to a number of well-maintained “letterboxes.” But the game really took off after May 2000, when President Clinton discontinued “selective availability” of public GPS signals, essentially allowing military positioning systems to feed personal navigation devices, thereby making them degrees of magnitude more accurate than they had been. That important shift was followed by a 2007 decision to launch GPS III, a new generation of positioning satellites designed to provide the free global utility we now rely on. This led, as any Google user knows, to maps with Borgesian (or Orwellian) levels of detail and mutability.

The call-and-response of the modern game’s online component—players publish coordinates of caches, log finds, thank hiders—makes it both a symptom and an enabler of the new techno-social age. It can be played over a lunch break, on business trips, virtually on Second Life, or as a seven-day Pacific sail to Suwarrow, in the Cook Islands, to a treasure that “may require some surf wading during high tide and some climbing” and that has been found four times. For me the game’s draw lies in its revelations—and in its ability to stave off, however superficially, the great existential question of where we are going and why.

Given a puzzle, the brain seems to sift through accumulated data on its own. Standing in Union Square, mine suddenly washed “a-ha!” over all my synapses. The sign! And there, stuck to the backside, was the magnet. It was graphite black, a thin-thread screw-top tube, as invisible as a bolt. I grabbed the pellet and unscrewed it. Tucked inside, a thin strip of tightly-rolled paper carried a list of marks, some cryptic, some plain: “etsijäpetteri, Regards from Finland,” “FrankChasti, Too much going on to be noticed,” “TFTC” (thanks for the cache), “#7805-7868.” I added my username and the date to prove I’d been there, returned the register, and sealed the hollow scarab. Then I restored it to its hiding spot.