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サフィル (Safiru), CC BY-SA 4.0, via Wikimedia Commons
Honzawa Onsen
本沢温泉Nagano · Chubu
本沢温泉 is a mountain hut at 2,150 m on the flank of Mount Io in the Yatsugatake range, walk-in only, running year-round. Its outdoor bath Un-jo no Yu ('bath above the clouds') is published as Japan's highest-altitude open-air hot spring — a simple wooden tub set directly into the scree slope, filled with milky sulfur-rich water piped straight from the source. A second bath, Kokemomo no Yu, draws on a different spring with a different mineral profile, indoors at the hut itself. The hut traces its opening to the late Edo period; the current building has stood since 1892 (Meiji 25) under the same Harada family, now three generations in and 144 years running a hut on this mountain.
- Best season
- Year-round
- Crowd level
- Hidden gem
- Admission
- ¥1,000 day-bathing fee for Un-jo no Yu (雲上の湯), ticket bought at the mountain hut's own shop before use. No published day-rate found for the second bath, Kokemomo no Yu (苔桃の湯). No tattoo policy is stated anywhere on the operator's own site — this row is NOT tagged tattoo-friendly.
- Website
- yatsu-honzawaonsen.com
Today
¥1,000How to get there
Reachable only on foot: from the Minotoguchi trailhead on the Yatsugatake range, walk in to the mountain hut (roughly 2-2.5 hours by the standard route). No road access. Reserve by phone, 090-3140-7312, reception 7:00-18:00.
Tags
onsenhiking
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