Onsen OniOnsen Oni

Sainokawara Rotenburo

西の河原露天風呂さいのかわらろてんぶろ

Bathing Complex
Kusatsu Onsen
Kanto·Gunma
0279-88-6167onsen-kusatsu.com

Day Use

Yes
07:00–20:00

4/1-11/30 7:00-20:00 (last admission until 19:30) 12/1-3/31 9:00-20:00 (last admission until 19:30)

Bathing & Water

Outdoor BathYes

Open-air outdoor bath

Indoor BathNo

Enclosed indoor bathing area

SaunaNo

Dry heat sauna room

Cold BathNo

Cold water plunge bath, typically used after sauna

OnsenYes

Uses natural hot spring water

Capabilities

Private BathNo

Private bath available for day-use visitors or hotel guests to reserve

Room OnsenNo

Private onsen bath in guest rooms, for overnight guests only

Mixed BathingYes

Shared bathing area for all genders

Mixed bath day Every Friday from 17:30 to 20:00, the open-air bath for men becomes a mixed bath! *Excluding specific days

Policies & Services

TattooYes

Allows entry with visible tattoos

KidsYes

Welcomes children and families

DiningNo

Restaurant or dining open to visitors (not just hotel meal plans)

WashingNo

Shower, wash stations, soap and shampoo provided

TowelsYes

Towels available to rent or borrow

Rest AreaNo

Relaxation space for after bathing

ParkingNo

On-site or nearby parking available

Water treatment

Pure source-flow
from Article 18 disclosure
  • Added water
    No
  • Reheated
    No
  • Recirculated
    No
  • Disinfected
    No
  • Bath additives
    No

草津温泉 万代鉱源泉

Kusatsu Onsen Bandaiko Spring

Operated by · 西の河原露天風呂

酸
Acidic
+ Sulfate · Chloride

Kusatsu's Bandaiko source — a 94.6 °C top-decile hot spring with pH 1.7, among Japan's most strongly acidic waters. A hydrogen-led acidic sulfate-chloride spring, it carries the sharp, prickly bite that defines the kusatsu style and has a long track record on stubborn skin conditions such as atopic dermatitis. With 26.4 mg/kg of free hydrogen sulfide layered on top, it also carries the unmistakable rotten-egg note of H₂S.

Source temperature
94.6°C
Hot
Tonicity
2.73g/kg
Hypotonic
Free CO₂
26mg/kg
Low
Free H₂S
26mg/kg
Very high
Highlights
  • Ultra-acidic
  • Top-decile hot

Analyzed Jul 1, 2023·群馬県薬剤師会·Cert no. 群馬県第2号

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SL
Slava
2 years ago

Meanwhile — Kusatsu Sai-no-Kawara. One of the must-visit higaeri onsens in Kusatsu. This is an enormous pool of onsen water. Sulfur, acidity. Because of its size, you get a temperature gradient from "I'm now a boiled lobster" to "I could sit here all year." You need to walk a bit from the center to get there, but it's absolutely worth it. On Fridays there's mixed bathing (konyoku) on the men's side.