A sulfur spring of the Shirahone Onsen area — a calcium-magnesium bicarbonate-chloride water of the hydrogen-sulfide type. It carries free H₂S and bisulfide with the characteristic rotten-egg note, the kind of sulfur water famous for turning milky-white once it meets the air. Neutral in pH and moderately mineralized at 1,108 mg/kg dissolved solids, it has noticeable body. The source is also one of the rarer ones approved for drinking, with the certificate listing benefits for gastroduodenal ulcers and high cholesterol.
Source temperature
36.0°C
Warm
Tonicity
1.11g/kg
Hypotonic
Free CO₂
300mg/kg
Typical
Free H₂S
4.70mg/kg
High
Highlights
Sulfur-rich
Analyzed Aug 18, 2015·一般社団法人 長野県薬剤師会·Cert no. 長野県第2号
About
Awanoyu sits in the Shirahone valley of the Japanese Alps, and the water here is what draws people: milky-white and faintly carbonated, rich in calcium and magnesium bicarbonate, with a bottom you cannot see. The big mixed outdoor bath (konyoku rotenburo) is the heart of the place: women enter from a separate changing room, walking in while already submerged, and thick bath towels keep things comfortable. The inn itself dates to 1912, classic wooden construction set in national park forest, and the sulfurous smell hits you before you even step off the bus.
Stayed as a ryokan guest. The place is absolutely amazing. The surrounding area is also cool — you can encounter wild monkeys. The food was great too. If you book a double room for one person, you can ask for a double kaiseki and they'll honestly give it to you.
As for the baths: in the main area (men's side), there are two indoor baths. One with clear water and below-average temperature, the other milky and hot. There's also a small additional third outdoor milky bath with below-average water temperature.
The main feature of the ryokan is of course the large mixed outdoor bath. I didn't take photos — there are plenty on Google, the internet, and even in the Matsumoto museum. The water is densely milky in color with a noticeable smell, and the temperature in the mixed bath is mild. You can honestly just hang out there for hours, moving around the bath and under the water streams. You really need to book a room with an overnight stay. At night it's absolutely heavenly to lie in the big bath all alone, snow all around, stars on the black sky — like something out of a fantasy.
Since you end up spending hours in the bath, the changing crowd can actually add variety. At one point in the evening, a grandma shooed out a grandpa and about 5-6 young Japanese women, directing their movements around the bath. The women are given bathing clothes, so everything is decent. For men — because of the dense milky water, nothing is visible, and entry/exit is also relatively modest.
If you compare baths head to head, this one is of course the best out of all 45 onsens/ryokans on this trip.
