The hunt is on. You've got your coordinates. You've pored over maps. Your Global Positioning System (GPS) is fully charged and doing its thing, having picked up from six or more satellites orbiting Earth. As you traipse through the woods, you stare down at the small screen—or more specifically, the arrow on the screen that's hopefully pointing you toward a flag icon signifying where treasure awaits: a geocache.

DID YOU KNOW?
Caches have been placed in more than 200 countries around the world.

The booty you seek most often comes in the form of a metal or plastic box containing a logbook and mementos of all kinds. When visitors find them, they leave behind things to prove they were there and, once they return home, they'll write up their experience online—but first it must be found.

Since the U.S. government boosted the accuracy of GPS units in 2000 by no longer scrambling the signal for security, your GPS unit is accurate up to 20 or so feet. Just a few possible problems: There may be an imposing cliff between you and where you need to go, a stream that needs crossing, or a patch of poison ivy. Furthermore, you may have to leave the trail—something that could be detrimental to the environment.

Scott Dresser knows the drill. The Massachusetts-based geocacher has found more than 1,700 individual geocaches around the world in the last four years, and manages nine excursions himself. He's even worked with land managers in places like the White Mountains to be sure the prizes are placed in environmentally appropriate places. Here's his take on how to geocache efficiently—and responsibly.

Coordinate your efforts
Geocaching often starts in a decidedly non-woodsy environ: the Internet. The website geocaching.com has coordinates to thousands of caches around the world. Type in your ZIP code, or your home's GPS coordinates, and you can find the ones closest to where you live. Beginners may want to avoid excursions tagged "unknown mystery cache," as they often involve crosswords, cryptograms, or other mind games. And those dubbed "multi-caches" involve a succession of clues at various locales.

Gearing up
As for types of GPS units, "you want something that's handheld, durable, and waterproof," says Dresser. "I've dropped mine a thousand times and it still works great." The Garmin eTrex (handheld) and Magellan CrossoverGPS (a car/hiking hybrid) both offer topographic relief maps showing where people need to go and what incline might be in their way. Also, getting a unit that keeps a good "lock" on your position is key. "If you don't have a high-sensitivity unit, you could walk beneath some trees and—poof!—you lose your lock," says Dresser. Another consideration is making sure the device has routable mapping software that will identify trails and roads around you.

Cache, not trash
Many caches are tucked away off trails, which may not be environmentally sound. This is, in part, why many national parks do not permit the placement of caches on their land, and natural areas, like the White Mountain National Forest, geographically limit their use, says Dresser. There is a growing effort to more closely regulate their placement. It starts with a cursory check performed by representatives from geocaching.com prior to posting coordinates. Caches have to be on public land, and there is an effort to keep them away from more dangerous areas such as bridges or railroad tracks.

Furthermore, geocachers can often learn whether a given cache is appropriately placed by checking online for land manager approval. Past visitors will also mention online if the geocaches are hidden in places that seem environmentally detrimental. Red flags, Dresser says, include muddy areas prone to erosion, alpine regions where delicate and rare plants grow, nesting bird locales, and wilderness areas that, by federal law, should remain "untrammeled" by humans. But sticking to caches that are hidden close to trails is easy. For example, First Mass, New England's first geocache (now managed by Dresser), is in the woods—but just a few feet off the beaten path.