TO UNDERSTAND how this is possible, one must know something about the unwavering Japanese drive for authenticity. The Japanese have a word for hobby, but in practice the meaning is much closer to obsession. I once met a Tokyo housewife who fell in love with soccer after watching the Italian team Juventus play, and instead of supporting Japan's domestic soccer league, she took Italian and began traveling to Europe several times a year to attend Juventus matches. In July of last year, a Japanese psychiatric counselor broke the record for memorizing pi, reciting it to 83,431 decimal places. That almost doubled the previous record, also held by a Japanese man. And in May, Takao Arayama, 70, became the oldest person to summit Mount Everest, having bested by three days previous record holder Yuichiro Miura, the Japanese extreme-skiing pioneer who was the subject of the Oscar-winning 1975 documentary The Man Who Skied Down Everest.

When the Japanese apply this drive for the genuine experience to adventure sports, which invariably have roots elsewhere, they tend to go to the source. While a secretary in Tokyo might spend a year saving for a rafting trip to New Zealand, she will tend to overlook the rivers in her own country. "My first year, people who would travel overseas to go rafting said, 'There's whitewater in Japan?' " says Australian Ross Findlay, whose success as an outfitter in northern Japan has made him a media darling across the country. "But by the second year, we had just taken off."

Once a sport does gain acceptance here, the growth can be staggering, as evidenced by the ski boom that swept Japan during the real-estate-fueled bubble economy of the eighties and nineties. More recently, surfing has enjoyed a Pokemon-like burst of popularity. "It took off here because of two things: Kelly Slater and DVDs," says Yuki Tsunoda, editor of Flow, Japan's biggest surf magazine. "Once there was a star people could follow, and once they could see how the rest of the world was surfing, that was all they needed." There are now an estimated one million surfers in Japan, and the Association of Surfing Professionals, the sport's governing body, has been holding contests here since 1979.

"These people love youth culture, and surfing exudes that," says American John Shimooka, the Australia-based marketing manager for Quiksilver, while we watch the early rounds of the Quiksilver Pro. "And the Japanese surfers have gotten so good. Fifteen years ago, when we first started coming over here, they were still so honorable; the other guys were paddling circles around them. But now they're as ruthless as anyone."

If it seems that Japan is being swept by a wave of adventure colonialism, well, that's close to the truth. Though some Japanese entrepreneurs have been at the forefront—the first time I ever kayaked was at a Japanese whitewater camp with a Japanese instructor, and MontBell, Japan's leading manufacturer of outdoor gear and clothing, has been running rafting and climbing trips for 27 years—a lot of the energy has come from outside. In the five years since I returned to the U.S., a loose confederation of expatriate businesspeople and restless English teachers has begun a more organized push into the wilds, establishing bilingual guide services for cycling, climbing, rafting, and backcountry skiing, setting certification standards, and introducing both Japanese and foreigners to a Japan few knew existed.

"AT FIRST, I was just writing about the stuff my friends and I were doing," says Gardner Robinson, 35, a Portland, Oregon, native who's lived in Japan for nine years and runs OutdoorJapan.com. "But the more we wrote, the more we realized there were other people doing the same things." The site is now the leading resource for adventure travel in Japan, in any language.

"We're breaking down those notions that Japan is expensive and inaccessible," says Robinson. "It doesn't have to be. You can rent a car and stay in a guesthouse for prices comparable to those in the U.S. And skiing is so much cheaper here than in the States."

Japan's highest concentration of ski resorts is less than two hours northwest of Tokyo by train, around the city of Nagano. Host site for the 1998 Winter Olympics, Nagano sits at 1,888 feet above sea level, surrounded by four mountain ranges, known collectively as the Japan Alps, that shoot up 7,000 feet from the edge of town. In the winter, the jagged peaks scrape all the snow out of the frigid Siberian air masses that slam into them after passing over the Sea of Japan. The resulting dumps make the Alps the snowiest mountains in the world. In the summer, they're mist-shrouded and as green as British Columbia, filled with trails, crags, and hot springs. "The first time I saw this place, I couldn't believe it," says Dave Enright, owner of the Nagano-based adventure outfitter Evergreen Outdoor Center. "It's endless—the wild, wild East."

Three weeks into my trip, Enright, 32, a dreadlocked, six-foot-three avalanche instructor from Vancouver, agrees to take me to Mount Ogawa, Japan's premier rock-climbing spot. He meets me at Nagano's Ueda station, where two of his guides—Canadian James Robb, 30, and Frenchman Jan Erkelens, 27—are waiting in a small white van loaded with climbing gear.

We eventually find the trailhead and scramble through dense, wet forest up to a 50-foot cliff, where Enright leads a 5.9 route called Ogawayama Monogatari ("Mount Ogawa Story"). I climb about 30 feet before a light rain hits, making the rock too slippery to continue. But before I descend, Enright, who's belaying me, tells me to look back. On the other side of the valley, a dozen narrow, 100-foot towers called the Baby Pinnacles rise up out of the forest, wet and black against the green. Through the mist, they look like a procession of monks on a pilgrimage back to Nagano.

Like the rest of the valley, the pinnacles are covered with bolted routes. But during the three hours that we're there, we don't see another person—though I wonder how long that will last. Ten years ago, when rock climbing became an officially sanctioned competitive sport in Japan, there were an estimated 20,000 climbers, according to the Japan Free Climbing Association. That figure has since jumped to 50,000 and includes Yuji Hirayama, 37, who in 2002, with American climber Hans Florine, set the free-climbing speed record of two hours 48 minutes for the 2,900-foot Nose route, on Yosemite's El Capitan.