...a few hours
TRY LETTERBOXING Walk 100 paces to a boulder shaped like an armchair. Then head east (check your compass) until you spot a woodpecker's favorite tree. You're hot on the trail of treasure—and a thrilling sport. It's called letterboxing, a combination of hiking and puzzle-solving that started in England in the mid 19th century and is just now taking off in the States. Your goal: to locate a box containing a notebook and a unique rubber stamp. When you find the stash, you use the stamp to mark your letterboxing journal (proof that the hunt was successful) and you leave an imprint from your own rubber stamp on the found notebook—which you return to the box for the next seeker. Over time, your journal will resemble a passport, recording your explorations.
Because you can pick hikes that match your children's abilities, letterboxing is perfect for families. (It's not to be confused with geocaching, a hide-and-seek game that requires a GPS device.) Letterboxing.org, the sport's nerve center, lists clues for some 14,500 boxes scattered across North America, with concentrations in the Northeast, along the West Coast, and in Texas, Ohio, Virginia, Mississippi, and Michigan (Marquette, on the Upper Peninsula, is shown below). Most boxes are planted by locals who want to share a favorite spot, so your family may end up on a secret beach in Cape Cod, or even standing behind the Hollywood sign—places you might never discover on your own. But there's no need to venture far. With an average of 100 new letterboxes placed weekly, it's likely there's one hidden near you.
In addition to providing clues for the majority of letterboxes hidden on the continent, Letterboxing.org addresses such pressing questions as how to use a compass and how to make a stamp (most people carve theirs out of an eraser). The Letterboxer's Companion ($15; Globe Pequot Press), by site co-founder Randy Hall, is another useful resource.