Akashi Onsen

赤石温泉あかしおんせん

Other
Chubu·Yamanashi

Day Use

Yes

Bathing & Water

OnsenYes

Uses natural hot spring water

Capabilities

Mixed BathingYes

Shared bathing area for all genders

赤石温泉

Akashi Onsen

Operated by · 保坂 卓

Sampled at wellhead
Acidic
+ 含鉄(II,III)泉 · 単純冷鉱泉
Classification

Hydrogen-Calcium Sulfate spring

A sharp, prickly acidic spring (pH 2.5 at the source) that is also markedly iron-rich, oxidizing reddish-brown on contact with air. At the wellhead the water carries a red tint with a strong metallic iron note in taste and smell. With total iron around 30 mg/kg it bites a little on the skin, and as a cold-mineral source below 25 °C it is reheated for bathing.

pH
2.50
Acidic
Source temperature
12.2°C
Cold mineral
Tonicity
0.50g/kg
Hypotonic
Flow rate
4.1L/min
Low
Free CO₂
52mg/kg
Low
Color
red and transparent, with a slight sediment
Taste
strongly metallic
Odor
strong metallic iron odor
Highlights
  • Ultra-acidic
  • Iron-rich
  • Cold mineral

Analyzed May 21, 2024·株式会社 山梨県環境科学検査センター·Cert no. 山環温2024-2号

Programs

About

A handmade hidden spring in the mountains of Yamanashi, built and maintained by the husband-and-wife owners themselves, from the entrance gate to the bathtubs. The outdoor pool is a reddish-brown acidic cold mineral spring (pH 2.2) that stains the rocks with rust-colored deposits; temperature shifts through the day, so the water can range from cool to lukewarm. Mixed bathing in the rotenburo is only on weekends and holidays from April through November.

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SM
Sergey M
1 year ago

545. 赤石温泉, Fujikawa, Yamanashi ★★★ Visited for higaeri at 800. Higaeri hours are listed as 09:30 to 16:00 (no info on specific days online, but they said by phone that higaeri is weekends only — yet they let me in on Monday for the indoor bath). They stamp the Yamanashi 100 Onsen book. Listed among the Hitou ("secret hot springs"). There's an amazing rotenburo and an unusual indoor bath. During my visit, only the indoor bath was available for higaeri. Unusual indoor bath. Inside is really cool and atmospheric. According to the schedule, it alternates between men and women in short time slots. The changing rooms are separate but both lead to the same bathing area. It may have been mixed bathing before. One bath with clear slightly murky brown water, temperature around 40. Breathing inside is good. The rotenburo is located separately from the ryokan building and looks amazing. They didn't let me use it (it was either being cleaned or something else — I couldn't understand due to the language barrier). But the owner gave me a very detailed tour of the men's rotenburo, and then the women's one too. The women's one turned out to be about three times smaller and simpler-looking. Great place. With its old-school vibes, friendly Japanese staff, and interesting onsens — I immediately wanted to stay overnight here. I'd recommend considering it for both accommodation and higaeri. But getting there won't be very convenient without a car. 12.05.2025