Right Onsen › Gunma › Tomioka

Oshima Kosen

Name: Oshima Kosen
Address: 148 Oshima, Tomioka, Gunma 370-2335, Tomioka, Gunma, JP
Telephone: +81274-62-1490
Rating: 4.2

4.2★ · 165 Google ratings · Tomioka, Gunma · 大島鉱泉

Open in Google Maps Official site (Japanese)

✓ Natural hot-spring water✓ Free-flowing source water

Before you go

Can you bathe here?

Day visitors

✓ YesOpen to walk-in day visitors for a flat admission fee, with no residency or membership requirement mentioned.stated by 3 visitors · Apr 2025 – Jul 2026

Hours

13:00–19:00from the facility listing

Price

¥450Ten separate reviewers confirm the entry fee is a flat 450 yen for adults.stated by 10 visitors · Dec 2024 – Jul 2026

Bathing arrangement

Men and women separateMen's and women's baths are separate, though the women's side has occasionally needed to be prepared on the spot for low demand.stated by 2 visitors · Mar 2026 – Aug 2026

Tattoos

Not known · call aheadno policy stated in the 42 recent reviews we read or on the facility's website

How we know this

Watch out

Lockers

There are no lockers; clothes go in open baskets, so valuables are best left in the car.

stated by 5 visitors · Mar 2025 – Nov 2025

Lodging

Overnight lodging used to be offered but was discontinued because of COVID.

stated by 2 visitors · Sep 2025 – Jun 2026

The bath

What you’ll find

A century-old, tiny indoor mineral-spring (kosen) bathhouse in rural Tomioka, Gunma, with one small tub, basket-only changing room, and 450 yen cash entry, run across four generations of the same family, day-use only since it stopped offering lodging during COVID.

Indoor baths

1One review describes a single fairly-sized tub with four washing stations.stated by 1 visitor · Mar 2026

Cold bath

NoNo cold plunge bath is present; the single tub itself runs hot.stated by 1 visitor · Mar 2026

Lodging

NoOvernight lodging used to be offered but was discontinued because of COVID.stated by 2 visitors · Sep 2025 – Jun 2026

The water

Spring type

Mineral spring (kosen), yellow-tinted waterDescribed as Gunma's only kosen (unheated mineral spring), with distinctly yellow-tinted water.stated by 3 visitors · Apr 2025 – Jul 2026

pH 8One reviewer measured the water at roughly pH 8.stated by 1 visitor · Mar 2026

Heated

✓ YesBecause the source is a cold spring, the water is heated with a firewood stove before bathing.stated by 2 visitors · Apr 2025 – Sep 2025

Practical

What to bring

Soap & shampoo

✓ ProvidedMost reviewers confirm shampoo and bar soap are provided, though one visitor advised bringing your own toiletries just in case.stated by 5 visitors · Dec 2024 – Jul 2026

Lockers

NoneThere are no lockers; clothes go in open baskets, so valuables are best left in the car.stated by 5 visitors · Mar 2025 – Nov 2025

Hair dryer

✓ YesA hair dryer is available, though one reviewer found it barely functional.stated by 3 visitors · Sep 2025 – Nov 2025

Guide

What visitors add

Price

Admission is 450 yen for an adult (one reviewer notes this price as current as of end of June 2026).

stated by 12 visitors · Dec 2024 – Jul 2026

Towels, soap & lockers

Soap and rinse-in shampoo are provided free (6 reviews confirm); one reviewer nonetheless advises picky bathers to bring their own bath set. No reviewer mentions towels.

stated by 7 visitors · Dec 2024 – Jul 2026

The water

The water has a strong warming after-effect: 5 distinct reviewers report staying warm or sweating well after the bath.

stated by 5 visitors · Apr 2025 – Mar 2026

Water handling

Not a hot spring flow: the source is a cold mineral spring (kosen) welling up behind the building, heated with a wood fire; one reviewer specifies water is added (kasui) and heating (kaon) is used, and another says the fire is stoked after guests arrive, so the bath can start lukewarm.

stated by 5 visitors · Apr 2025 – Jan 2026

Towels, soap & lockers

There are no lockers or valuables boxes, only open baskets; reviewers advise leaving valuables in your car (5 reviews).

stated by 5 visitors · Dec 2024 – Mar 2026

Towels, soap & lockers

There are no showers: washing stations (4 of them) use old-style separate hot and cold push taps and you mix water yourself in a basin (5 reviews).

stated by 5 visitors · Apr 2025 – May 2026

Timing