When my family moved from the woods of western Massachusetts to southwest England about a year ago, we knew we were headed for Hound of the Baskervilles territory, a land of brambly hedges, thatched cottages, and legendary moors. What we didn't know was that moving to a town on the edge of England's Dartmoor National Park would land us right in the birthplace of the letterboxing craze -- and turn us into stealthy sleuths to rival Sherlock Holmes himself.

For those of you who don't already know, letterboxing (like its high-tech cousin, geocaching; see our sidebar on Letterboxing Lingo) combines hiking with the added element of treasure hunting. Participants get clues online -- they might be straightforward directions, clever riddles, or something in between -- then follow them to hidden boxes containing a logbook, an ink pad, and a rubber stamp. Upon discovering one, you document the find by "stamping in," marking the box's logbook with your own rubber stamp and a brief message, and stamping your own logbook (a passport of sorts) with the box's stamp.

Letterboxing got its start in the mid-1800s, when Englishman James Perrott placed a glass jar within a mound of stones at Cranmere Pool, a remote spot in Dartmoor. People who made the arduous trek after him could prove they'd been there by leaving their calling card in the jar. Perrott's idea took hold and spread throughout Dartmoor and, eventually, beyond. In 1998, an article in Smithsonian helped spark interest in the hobby outside of England, and today there are thousands of letterboxes around the world, including more than 23,000 in the United States. In fact, it turns out my family had been hiking right past plenty of letterboxes during our eight years in Massachusetts. With some in every state, chances are many other families have done the same.

The whole idea of letterboxing had instant appeal for my husband, Chris, and our kids, Maddy, age 10, Oakley, 7, and Julia, 4. Here was our chance to be Harry Potter searching for the Sorcerer's Stone, Indiana Jones in pursuit of ancient treasure. By the end of our first day, our logbook was filled with stamps, including two different butterflies, a horseshoe, and a Dartmoor pony.

We were hooked. Besides being a fun excuse for families to get outside and get moving, letterboxing hunts come in a wide range of lengths and difficulty levels, making them a great activity for Scout troops and other groups as well. Tracking down the hidden boxes also offers a sense of accomplishment, the thrill of the hunt, and the excitement that comes with exploring new territory. Here's how to plan your outing