Two paths diverge in a muddy wood, and the first team to reach the junction zigs right. Glancing quickly at my map without pausing to break stride, I zag left along with my teammates, Adrian and Nevin. The first checkpoint is at the top of a tree-lined ridge in the distance, and our route looks like the quickest, most direct approach. As we push on, Adrian glances back over his shoulder at the stream of runners reaching the crossroads behind us — every one of whom is turning right. "Um," he pants, "should we be worried about this?"

We're barely 10 minutes into a race called Raid the Hammer, which is — in theory — about 15 miles long. But there's no actual course. Instead, there are 38 checkpoints stashed among the dense forests, vertiginous cliffs, and shoe-sucking swamps of a 3,000-acre conservation area near Toronto. We have to hit them all in the right order, using only a compass and the maps we were given just before the start. The organizers say it should take between three and seven hours — depending as much on our route choices as foot speed.

Orienteering is the original adventure race, the granddaddy of the current wave of pseudo-military obstacle courses like Tough Mudder, Warrior Dash, and Spartan Race. The sport was introduced to North America by teams at West Point and Quantico Marine Corps Base in the 1960s and flourished both in and out of military circles for a few decades before a long slide into obscurity. "There are lots of trail runners and adventure runners who have never really thought about orienteering," says Raid the Hammer race director Mike Waddington. But they're catching on. Participation is now growing by about four percent a year, according to Glen Schorr, the executive director of Orienteering USA. Last year, races across the country registered about 50,000 entries.

Adrian and I are prime examples of the sport's new recruits. We're both experienced road and trail runners looking for a new fix. (I was the fourth-ranked miler in Canada in 1997, and, like Adrian, I have since competed at world championships in cross-country and mountain running.) But we also have a purist streak: no obstacle courses, thanks. Nevin, who has competed in orienteering races since he was a kid, lured us in with a simple pitch: It's an old-school, hardcore trail race without a trail. No gimmicks, no man-made barriers — just you against the terrain. We're off to a rough start, though. We emerge from the forest to find a dense, neck-high field of thistles blocking our path. It's now obvious why most of the other runners turned right instead of following our "shortcut" to the left. By the time we fight our way through the thistles, we've lost some blood — and almost seven minutes to the leaders.

There are digital checkpoints along the course marked by a small orange-and-white flag; instead of the traditional stamps or hole punches, we insert a small chip into a digital reader to register the exact time we pass. The first checkpoints are relatively easy to find, but as the race progresses, the terrain gets hillier, the forest grows thicker, and the trails we've been following gradually disappear. It isn't just about figuring out which direction to go, says Col. Mike Hendricks, the head of the orienteering program at West Point. You also have to learn to assess terrain on the fly, so that you know instinctively what to go over, around, or through. Our bumbling progress through the woods is typical of what Hendricks sees each fall in his cadets: "You can hear a new cadet just smashing through things."

With practice, Hendricks' charges learn to travel more efficiently. "Usually, these kids are in pretty good shape. Their issue is that they're going too fast in the wrong direction," Hendricks says. "The classic thing is you're running like crazy, but you keep meeting the same 50-year-old lady at every checkpoint, because she's more efficient." His words ring painfully true: At one point we pass the same team — older, slower, and co-ed — three different times, thanks to a series of wrong turns.

We finally stumble across the finish line, after three hours and 54 minutes. Despite being the fastest runners in the field, we end up almost 49 minutes behind the winners. Clearly there's a skill here that we're missing. There's no simple answer to choosing the right path while navigating under pressure, Hendricks tells me. The best teacher is experience. So I drive home, nursing my scratched arms, aching legs, and bruised ego, and sign up for the next race in the series.

This Summer's Top Orienteering Races

Here are **six competitions where you can test your map skills across the country.

**TBD: Western Mass, Amherst, MA

The nationally sanctioned 4K at Mount Holyoke Range State Park sweeps the 1,000-foot mountain.

6/7: Jug Bay, Lothian, MD

Free beginner instruction is included with entry to Jug Bay, held about 30 miles outside D.C.

5/30: Rochester Map Adventure, Rochester, NY

There are seven courses at 150-acre Highland Park, from 1.5K to 9K, for all levels of orienteering.

7/11: MNOC Adventure-O, Minneapolis, MN

Teams compete for six to eight hours in this race that includes running, paddling, and biking.

8/22: RMOC, Lake George, Colorado

Get lost near Blue Mountain in this tough, mile-high race outside Colorado Springs.

**TBD: Laramie Daze, Laramie, WY

This competitive 5K orienteering run takes place in high-altitude shortgrass prairies.

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