A GPS unit does not, however, do all the work. Most caches are so well hidden, you could walk right past one every day and never notice it. Caches are even assigned a difficulty rating—1 through 5—based on where they are stashed and the mileage required to reach them. (A close-in cache in Forest Park might get a “1”; one requiring a four-mile hike into the Mt Hood Wilderness might warrant a “5.”) While geocaching with my girls, we’ve had to climb trees to peer inside squirrel holes and peek underneath mossy rocks. We even paddled out to Wells Island in the Columbia River to trace a container hidden by thick blackberry bushes.

Of course, you won’t uncover Long John Silver’s pieces of eight in these secret chests. The waterproof canisters, usually heavy-duty Tupperware or old military-surplus ammo boxes, often contain little more than a logbook to sign and a slew of tiny trinkets: refrigerator magnets from Route 66, Here Today Gone to Maui key rings, or bar coasters from Deschutes Brewery. The main rules when you find a cache: Take something, leave something, sign the logbook, and re-stash the box. Or, if you’re like me, just scribble “TNLN” (“Took nothing, left nothing,” in geocache vernacular).

Which isn’t to say that I walk away empty-handed; geocaching gives me practice at using my GPS, something that makes me a better Crag Rat. Just last spring, a call woke me at midnight: A family with two young children was lost on Mount Defiance, a 5,000-foot peak near the Gorge. When I got there, we had a rough idea of their whereabouts thanks to coordinates radioed in from a spotter plane that had buzzed the search area at dusk. But the moonless night made taking a compass bearing nearly impossible. Instead, I plugged the coordinates into my GPS and let the faint glow of my now-trusted hiking companion guide my team methodically and efficiently up a steep, trail-less hillside to the family. By sunrise all of us were back at the trailhead, chilly and wet, but unhurt.

But the greatest treasure geocaching has given me? The adventures I share with my daughters. Every time they unlatch the lid to another find and I see their faces light up as if they were a pair of budding Nancy Drews who’d successfully solved another mystery, I can’t imagine what we did for fun on the trail before.