Outside the car windows the landscape was a textured patchwork: winter orchards, rice paddies and tile-roofed farmhouses all stitched together by the threads of narrow roads.

I kept one eye on the way ahead, but the other was caught by the repeating monochrome pattern of bare apple branches against the off-white of last week’s snow. The hills in the near distance were white and gray with snow and leafless trees. A ragged horizon serrated the clear winter sky.

By train or on the expressway, Yudanaka is only an hour north of Nagano city, capital of its eponymous prefecture, but on the back roads it’s a slower trip, and it was nearly evening when the three of us — my mother, sister and I — arrived in the quiet town.

The narrow streets were empty and darkening with early dusk, the streetlights were coming on, and our ryokan (traditional Japanese inn) looked like the most welcoming place in the world, with its shoji (sliding, paper-paneled doors) softening the warm yellow light escaping through the windows.

It wasn’t much of a ryokan: the tiny room was threadbare, and a poorly behaved Akita dog jealously guarded the narrow entrance, harassing us at each arrival and departure. So, when we set out to explore the locale, we tied our shoes hastily in the chilly blue darkness.

Yudanaka is an onsen (hot-spring) town, and the air was slightly sulfury. It’s an old area. Seven hundred years ago, monks bathed here; 500 years ago a warlord named Takeda Shingen used the hot springs just upriver at Shibu Onsen to heal his men’s battle wounds. Even now, bathing in all nine of the town’s historic springs — housed in quaint wooden buildings along the narrow old road and in blocky, bubble-era concrete ones along the river — is reputed to cure all kinds of ailments.

In truth, it’s not much of a place to write home about, being quiet and mostly concrete. Other than visiting the onsen baths, there’s little to do after dark. In the end we downed a quick dinner of ramen at the only open restaurant we could find, and ventured forth once more, warmed from the inside, into the snowy night.

Though seven of the nine public baths in Shibu Onsen are, charmingly, free to use, we stopped at a closer one near Yudanaka railway station as we were intent on starting early the next day.

Too cold for yukata (cotton kimono), stopping at the baths meant bundling out of winter coats and several layers before we could steam contentedly in the waters. The big bathhouse was easily the busiest place in town, but we didn’t stay long: we had come for a very different bathing culture foremost in our thoughts for the following day.

For good reason, there’s no road to the area’s main attraction, and the next morning we drove up to a parking lot that looked like the last stop before the wilderness. In the falling snow the three of us slipped and scrambled breathlessly up a narrow path through a dark forest of towering firs. A stylish woman in stilettos strode past and vanished around a corner as we watched, quite baffled.

The Earth’s veins run close to the surface in much of Nagano Prefecture. Walking past an old wooden onsen inn with its outdoor baths, and the geyser’s calcified metal spigot made the delicate geothermic balance perfectly clear. The air was eggy with the smell of sulfur. It’s no surprise that they call this place — narrow and in nearly perpetual shade during the winter months — Jigokudani: Hell’s Valley. It is famous, however, for something else entirely.

We had come because of a book. For years, a glossy tome on Japan’s wildlife had occupied an honored spot in my mother’s bookcase, and, among stunning photographs of courting cranes and soaring sea eagles, all three of us had been fascinated most of all by the images of “snow monkeys.”

Populations of red-faced, short-tailed Japanese macaques live throughout Japan, from Kyushu to northern Honshu (though not in Hokkaido), but the monkeys at Jigokudani Monkey Park are the nation’s best-known troupe. They’ve been on magazine covers and in countless books like the one that had drawn us here; they are, indeed, likely the most famous macaques in the world. Why? Because they bathe.

Minutes after paying our entrance fees, we were standing face to face with the most contented-looking monkey I’d ever seen. A large male, who, by his closed eyes and the relaxed expression on his face, seemed to feel secure not only with his status in the troupe, but also by being immersed in steaming-hot rotenburo (open-air hot-spring) water.

With his arms resting on the stone wall, he was an uncanny, pink-faced imitation of any human bather. I was fascinated, unnerved and unsettled. The gap between us and our simian relatives was clearly much narrower than I had ever really appreciated.

This gap, and indeed, the behavior of Japanese macaques in general, is well studied. Ever since the 1950s, scientists have been nearly continually observing — and, to make this task easier, feeding — several troupes of macaques. Over the same period — probably because they’ve got lots of free time now they don’t have to gather their own food — these groups of macaques have developed something that can only be called “culture.”

A group of them in Kyushu, famously, began washing their potatoes, and other troupes throughout the country use their free time to make something akin to music, by banging stones together. Though both are fascinating, it was the more picturesque culture of the Jigokudani macaques that caught the world’s attention.

Hot-spring waters come out of the ground at temperatures ranging from boiling to downright cool. At their source, the Jigokudani onsen waters are scaldingly hot — far too hot for either humans or monkeys to bathe in.

But not long after the water temperature at the nearby ryokan was adjusted for comfortable bathing in the early 1960s, a young macaque waded into a newly built rotenburo to retrieve some food. She stayed to enjoy the warmth, and the behavior soon became popular each winter throughout the troop.

Now they have their own baths and they draw thousands of visitors from Japan and abroad, there being few places in the world that you can observe wildlife taking its ease at such close range. And there is no other place where you can watch “hot-spring monkeys” bathe in a seemingly effortless imitation of their smooth-skinned cousins. It is very hard to look away: The mirror of evolution is captivating and well worth the visit.

Getting there: Yudanaka Station is an hour from Nagano by express (¥1,230) on the Nagano Dentetsu Line. Though the monkey park and a quick bath (or foot bath, by the station) can be squeezed into a day trip, it’s worth staying in the charming upriver town of Shibu Onsen. For those looking to really immerse themselves in the wildlife experience, travelers are occasionally joined by macaques in the outdoor baths by the Korakukan Jigokudani ryokan ([0269] 33-4376), which also serves traditional Nagano cuisine.

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