I feel my way along the tunnel; it’s pitch black and narrow, and all I can do as I inch forward is grope for the spot. Hidden below the altar of the Zenkoji Temple’s main hall is, so legend has it, the key to enlightenment. Those who feel it achieve satori. My hand glides over some­thing on the wall; it is smooth, long and cylindrical, and made of metal.

Outside, snow is steadily falling on Nagano city, tempering the incense-filled air. If enlightenment means having discovered, as a non-skier, the delights of Nagano prefecture in winter, then it doesn’t really matter whether I’ve just touched the elusive key or not.

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A few days earlier, I walked into Nagano prefecture, in central Japan, over the Magome Pass, with a guided tour group. Whereas the western side, in Gifu prefecture, had been snow free, as soon as we crested the pass and entered Nagano, we were in a world of snow and ice.

The Nakasendo was one of the few officially sanctioned communication routes under Tokugawa shogunate-ruled Japan (1603-1867) and linked the power base of Edo, modern-day Tokyo, with the nominal capital, Kyoto, where the emperor resided. Along the way were 69 staging posts.

With the coming of the railways, these posts fell into obscurity, to be given a new lease of life only recently, by tourism. In the summer, towns such as Tsumago heave with tour groups but, as we kneel on the tatami around an irori fireplace in its waki-honjin (the second-best class of inn), smoke rising into the hinoki cypress beams overhead, we find ourselves alone. It must have been much the same when the Meiji emperor stayed here in 1880.

Matsumoto, Nagano’s second-largest city, is 100km or so further along the Nakasendo Trail and, being easily accessible from Tokyo and Nagoya, is seen as a convenient gateway into the prefecture.

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Japan is full of castles but most of them are concrete reconstructions. Crow Castle, as it is nicknamed, thanks to its black hue, is the real deal. Perched on a moat with the Japanese Alps in the distance, it is still very much the symbol of Matsumoto, even though the city centre has migrated a few blocks to the south. The castle’s donjon holds a secret; from the outside the fortified tower appears to be five storeys high but it is, in fact, six, with a hidden third floor, which was used as a strong room to garrison troops in during wartime. However, the castle, the construction of which began in about 1593, has not seen much strife, and therefore possesses more aesthetic elements, such as a moon-viewing wing.

Old-town Matsumoto comes alive on Nawate and Nakamachi streets, around the Metoba River. Nakamachi, in particular, has a lot of old black-and-white storehouse-type buildings, known as kura. Today, they house souvenir shops and restaurants selling soba, the buckwheat noodles that are a Nagano speciality, thanks to the abundant clean water in the province.

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In Matsumoto, instead of being served cold, soba are heated in a mushroom soup – just the thing to ward off the winter chill. Deep-fried chicken is also popular, in the form of sanzoku-yaki, wherein the meat is marinated in garlic and spice-laden soy sauce.

Even those with little knowledge of Japanese art might recognise the works, if not the name, of Katsushika Hokusai. Were it not for Japan’s foremost woodblock artist spending his later years in Obuse, there might be no reason to visit the prefecture’s smallest town, which is about 80km north­east of Matsumoto.

Hokusai didn’t make his first visit to Obuse until his 83rd year, at the invitation of a local intellectual, Takai Kozan, but he would return three times, finding the town conducive to his craft and leaving behind a large body of work. Hokusai Museum houses more than 40 paintings he produced here, along with the ceilings of two floats he painted. These floats were paraded through the streets of Obuse during shrine festivals.

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Followers of the artist should also visit the Ganshoin Temple, on the east­ern side of the town, where the main hall ceiling features a magnificent painting of a phoenix that incorporates 4,400 sheets of gold leaf along with other precious min­er­als. At 30 square metres, it is Hokusai’s largest work and was completed when he was 89.

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Hokusai’s legacy continues to attract artists and artisans to Obuse, other notable collections of which include those in the Japanese Lamp and Lighting Museum and the Contemporary Chinese Art Museum. The Takai Kozan Museum features the studio he built for Hokusai.

Local characters of a different sort are encountered about 20 minutes from Obuse by train, outside Yamanouchi, which is known for its snow monkeys.

Resident in the mountains above the town in ominously named Jigokudani (“hell valley”), the wild animals are, during the winter, lured to hot-spring pools by the food offered at the Jigokudani Monkey Park. Often standing in the snow surround­ing the pools, doing what they can to ward off the chill, are large numbers of people, the only primate to live at more northerly latitudes than the Japanese macaque.

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As the onlookers watch, a baby monkey coos on a post while clutching a piece of string. Nearby, three babies huddle together for warmth on a pipe while, across a stream, adults undertake the more serious activity of foraging, digging in the snow for what­ever they can find.

But take it from the monkeys, the best way to beat the cold is in an onsen – and, fortunately, the nearby towns of Shibu and Yudanaka have plenty that cater for human bathers.