Shirahone Onsen Awanoyu

Nagano’s biggest spring flow of carbonated sulphur water — the 70-tsubo milky bath open just three hours

Awanoyu, founded in 1912, is Shirahone’s flagship inn, and its roughly 230 m² milky-white “Large Open-air Bath”, made famous by posters and television, ranks among Nagano’s must-visit onsen. The “awa” (bubbles) in the name refers to the carbon dioxide dissolved in the ~38 °C source: step into the unheated indoor “nuru-yu” and fine bubbles cling white to your skin — above 40 °C the gas would separate, which makes a carbonated sulphur spring like this nationally rare. At 1,730 litres a minute, the largest flow in Nagano, even the huge open-air pool is entirely free-flowing without dilution, recirculation or disinfection, and the water, clear as it emerges, shifts from milk-white to cobalt blue with air and light. The big bath is mixed, worn with a bath towel, but a separate women’s entrance and changing room let you enter already submerged, and the opaque water makes it an oft-recommended “first mixed bath”. Day bathing is a three-hour window only — reception 10:30–13:30, out by 14:00 — closed Wednesdays and Thursdays outside the summer holidays, so planning around it is the key to a Shirahone trip.

Tips & cautions

- Day use is a three-hour window (reception until 13:00, out by 14:00). Closed Wed/Thu outside summer holidays, with ad-hoc and winter suspensions — phone first (0263-93-2101).

- Bath towels may be worn by everyone in the big bath; women enter from their own door already submerged.

- The real treat is the unheated 36 °C “nuru-yu”: 15 minutes or more and you feel the bubbles and the warmth. Alternate with the 43 °C heated tub.

- Sulphur and carbonic smells can cling to clothes; silver tarnishes.

- Crowded when tour buses arrive around 11:00 — go right at 10:30.

- No photography. Tattoo policy unconfirmed — ask ahead.

- Restaurant and shop on site. Staying overnight gives you the big bath at leisure in the evening and morning.

Getting there

Matsumoto Station → Alpico Kamikochi line to Shin-Shimashima (~30 min) → Shirahone Onsen bus ~70 min to the terminus “Awanoyu” (Azumi 4181, Matsumoto). 15 min by car from Sawando (Kamikochi shuttle base). By car ~1 h 10 min from Matsumoto IC via Route 158; free parking. Icy roads in winter.