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 http://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.
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.