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Unkai Kusushi Onsen

雲海薬師温泉うんかいくすしおんせん

Public Bathhouse
Kyushu & Okinawa·Kumamoto

Day Use

Yes
10:00–21:00
¥400

Bathing & Water

Natural onsen water

Uses natural hot spring water

Indoor BathYes

Enclosed indoor bathing area

雲海薬師温泉

Unkai Kusushi Onsen
Sulfate
+ Bicarbonate
Color
colorless and transparent
Taste
metallic
Odor
faint hydrogen sulfide

Sodium-Magnesium-Calcium Sulfate-Bicarbonate spring

pH 7.1NeutralHot source · 47°CHigh silicaSulfur-rich
Composition fingerprint1.3 g/kg dissolved · Hypotonic
Na⁺54
Mg²⁺22
Ca²⁺20
SO₄²⁻66
HCO₃⁻21
Cl⁻13
CationsAnions
Sodium Na⁺
salt's cation — pairs with chloride to make the water salty.
Sulfate SO₄²⁻
"gypsum / Glauber's salt" — vessels and wound healing.
Known good for
  • Aches & jointsstiff shoulders
  • Skin conditionsatopic skin, eczema
  • Circulationtired legs
  • Sensitive-skin cautionbroken or dry skin

A sodium-calcium-magnesium sulfate spring with a bicarbonate sub-type — settled, mineral-rich body with bicarbonate softness layered in. Neutral pH and 46.6 °C at the source, with metasilicic acid at 127.7 mg/kg leaving a thin silica film for noticeably smoother skin. A modest 18 mg/kg of free hydrogen sulfide gives the water a faint rotten-egg note and a metallic edge at the wellhead.

Sampled at mixing tank·Analyzed Feb 3, 2017·株式会社 再春館安心安全研究所·Cert no. 第K1600025-001

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Programs

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1 review

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Sergey M
1 year ago· edited

430. Unkai Yakushi Onsen, Aso, Kumamoto ★ An old-school onsen for ¥300 from the Aso association. The stated hours are 10:00 to 21:00. They stamp the Kyushu 88 onsen stamp rally. The bath photo is from the internet, and it matches. There was a funny moment. I walked up to the payment window, it was closed, nobody was inside, and there was no separate payment box either. So I thought I had to slide the glass at the window open and drop in the coins. I started opening the glass, and, as if on cue, a small hatch opened on the right wall inside, and an old man popped out. I said I wanted to pay, go into the onsen, and get the stamp. He said to leave the payment and go into the changing room. It turned out the old man was bored sitting at the cash desk, so he sits in the changing room of the onsen in his jacket and clothes to chat with visitors, since the changing room and the bath are basically in the same room. He took the stamp book and went to a separate room to stamp it, gave me credit for the number of stamps, and we chatted a bit about onsens as much as the language gap allowed. The indoor bath has cloudy whitish-green water, temperature 40-41. It is easy to breathe inside. A good place. 16.01.2025

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Last updated July 17, 2026