Three days is enough to taste Nagano's main flavours: a great temple, wild monkeys in hot springs, a samurai castle and a town of old streets. The plan below runs from Nagano city, uses trains and one guided tour, and flexes with the season.
Day one: Zenko-ji and the city
Start early at Zenko-ji, ideally for the morning service, when the priests chant and the crowd is thin. Walk the Niomon and Sanmon gates, enter the main hall, and do the Okaidan walk in the dark under the altar. Browse the shops on Chuo-dori on the way back, with a stop for oyaki dumplings and soba. In the afternoon, take a sake tasting walk or ride the bus to Matsushiro for samurai houses, the Sanada museum and the quiet streets. If your legs have energy, the Olympic sports park is a good alternative for sports fans. In the evening, join an izakaya tour or find a small pub near the station and order the local specialities.
Day two: the snow monkeys and a hot-spring night
Take the Nagano Electric Railway to Yudanaka in under an hour, then the bus to Kanbayashi Onsen and the forest walk to the park. In winter, the macaques sit in steaming pools in front of you, and a couple of hours is enough to take photographs and watch the troop. Return to Yudanaka and Shibu Onsen for lunch, and, if you have the time, stay overnight in the valley rather than returning to the city. A night in Shibu gives you lantern-lit lanes, a ryokan dinner and an early morning at the monkeys before the tours arrive. If you prefer to keep a single base, a guided day tour from Nagano combines the monkeys with Zenko-ji and sake.
Day three: Matsumoto
From Yudanaka or Nagano, take the train to Matsumoto. Spend the morning at Matsumoto Castle, arriving early to avoid the queue for the keep. Walk through Nakamachi and Nawate, stop for coffee in one of the old storehouse cafes, and visit the Old Kaichi School or the city art museum. Eat soba for lunch. In warm months you could replace the afternoon with a trip to Kamikochi, though that really deserves its own day. In the evening, return to Nagano or continue to Tokyo, Takayama or Kanazawa from Matsumoto.
The winter version
Add a ski day at Hakuba, Shiga Kogen or Nozawa, and drop Matsumoto if you need time. Winter days are short, so start early, carry hand warmers and give yourself buffer for slow buses. The snow monkeys are at their best, Togakushi is quiet and snow-covered, and onsen soaks are most rewarding. Kamikochi and the Tateyama Kurobe route are closed, so skip them.
The summer and autumn version
Swap the monkey day for Kamikochi, using Matsumoto as the base. The valley is open from spring to mid-November, with flat walks from Kappa Bridge to Taisho Pond. In autumn, add the Tateyama Kurobe Alpine Route for the leaves, or Togakushi and its cedar avenue. Obuse and its chestnuts are at their best in autumn, and Shiojiri's wineries are busy at harvest.
Practical tips
Buy tickets for the Shinkansen and limited express in advance in busy seasons. Carry cash for small shops and baths. Check the forecast each morning, because mountain buses, ropeways and valleys close in poor weather. Travel light and use luggage forwarding between cities if you can. Book hot-spring accommodation early, since the best ryokan and onsen hotels sell out.
Where to sleep
Use Hotel Metropolitan Nagano or Nagano Tokyu REI Hotel for the city night, Shibu Hotel for the monkey night, and Hotel Buena Vista or Tabino Hotel in Matsumoto for the castle night. If you add Hakuba, the Courtyard by Marriott or Hakuba Highland Hotel give you a base on the slopes.
Budget and booking rhythm
Three days can be done at a range of price points. Business hotels in Nagano and Matsumoto keep nights affordable, while the onsen night is the splurge worth making. Day tours cost more than going alone but save time and stress in snow. Buy rail tickets in advance for popular trains, reserve hot-spring accommodation early, and keep one flexible afternoon for weather or for something you discover along the way. Many travellers add a fourth day for Togakushi or Obuse, both of which suit a slower pace and a quieter mood.