Two hikers follow a rocky trail through a thicket of trees — but they're not on an ordinary walk in the wilderness.
They're on a treasure hunt, following a set of clues leading not to a cache of jewels, but to something called a letterbox.
Once they've managed to locate and dig up the buried box — which is actually a waterproof Tupperware or other plastic container — they'll find the treasure inside: a log book and an ink stamp used to document their success.
Letterboxing is like a scavenger hunt for hikers. Participants can log onto www.letterboxing.org or a number of other Web sites to find a list of clues that hikers can follow to find one of the thousands of boxes hidden out in nature all over the country.
"When you open the book, you've become a part of the gang of people who have been in that area and found that box," said Tim Brookes, a Vermont writer and NPR essayist who has written about the hobby.
Those familiar with the sport say it gives hikers an extra sense of purpose and a way for them to connect with one another.
"The appeal is that it's a challenge, it's a treasure hunt," Brookes said. "And it's a way of creating community in a solitary pastime: hiking."
The sport originated in nineteenth-century England, when a hiker decided to leave his calling card tucked inside a bottle in the Dartmoor countryside in 1854. Those who stumbled across it left cards too; eventually, walkers began burying waterproof boxes containing stamped postcards for the finders to send.
Letterboxing remained popular in England, but didn't catch on in this country until the 1990s, when a New England man used it as an educational activity for schoolchildren.
Today thousands of people participate in the hobby in the U.S. At last count, there were about 1,500 boxes hidden in the American wilderness. There are also boxes buried in Canada, Mexico and Costa Rica, among other countries.
But those interested in taking up the sport should be forewarned: finding the box isn't a sure thing.
"It's a lot harder than you'd think," Brookes said. "I spent two hours with my family looking for one."
Clues to boxes hidden in the U.S. are more compass-oriented, and many use degrees to guide the hiker — so bringing a compass is wise — whereas those in England are more map-oriented, said Oklahoma letterboxer Dennis Williams.
"It helps me hone my map and compass-reading skills," Williams said of the pastime. "And it gets me out into the wild, and I enjoy that. It's not just a walk-in-the-woods experience."
Part of the fun is the creativity and artistry involved in carving the ink stamps used to mark the log book and in writing the clues, which can range from the poetic to the downright cryptic.
"I try to think of creative stories to set the clues in to take the next person down the trail," said Williams. "There's a sense of mystery."
One set of clues to a letterbox buried in Liberty State Park in Jersey City, N.J., was done in rhyme.
"Now off the path, walk toward the sea, in the cairn between two trees is where your treasure will be!"
Williams, a professor of geography and history at Southern Nazarene University outside Oklahoma City, uses letterboxing as a teaching tool and assigns hunts to his students for extra credit.
"This is a wonderful way to introduce my geography students to using a compass and getting out in nature," he said. "I hope it makes them more observant and more curious about the world in which they live."
The letterboxing community has extended to the Internet, where many people post not only clues to boxes they've hidden, but e-mails about their experiences. And those who live near each other sometimes organize group excursions.
After all, finding buried treasure will always be an alluring prospect for the curious explorers among us.
"Letterboxing allows you to follow somebody else's footsteps and see the landscape in the way they did," Williams said. "You're actually getting into the mind of the clue writer. I find that historical voyeurism appealing."