Right Onsen › Gunma › Annaka
Kami-Masuda Onsen Toride-no-Yu
4.1★ · 353 Google ratings · Annaka, Gunma · 上増田温泉 砦乃湯
✓ Natural hot-spring water✓ Free-flowing source water✓ Outdoor bath✓ Rest area✓ Restaurant
Before you go
Can you bathe here?
Day visitors
✓ YesThis is a day-trip hot spring facility (higaeri onsen), commonly used by hikers.stated by 2 visitors · Aug 2025 – Dec 2025
Hours
11:00–19:00 · closed Wednesdayfrom the facility listing
Price
¥800Standard admission is ¥800 for a 3-hour visit; since a May 2025 update, a full-day pass costs ¥1000.stated by 5 visitors · May 2025 – Jun 2026
Time limit
3 hours (800 yen); full-day pass 1000 yenStandard entry is time-limited to 3 hours; a 1-day pass is available for ¥1000.stated by 5 visitors · May 2025 – Jun 2026
Tattoos
Not known · call aheadno policy stated in the 36 recent reviews we read
Watch out
Restaurant
An on-site restaurant exists but is unreliable: it has been closed during off-season/weekday visits, seems to mainly run weekends, and reviews split between praise (ginger pork set, tanmen) and complaints of high prices and poor quality.
stated by 9 visitors · May 2025 – Jul 2026Outdoor bath
An outdoor bath exists, but under the current owner its area has been cut to under half its former size and depth reduced about 20% (kerosene heating cost cited); reviewers also report ants and horseflies and unclear rust/mold debris in the tub.
stated by 6 visitors · Jun 2025 – Jul 2026Sauna
A sauna exists but only operates weekends/holidays and shuts off as early as 17:00-18:00; one reviewer measured a low 76-78C and warned the resulting cold-plunge shock could be risky for elderly visitors.
stated by 5 visitors · May 2025 – May 2026Rest area
A tatami rest room is available and spacious, but in cold months the changing room and rest room have had inadequate heating (one visitor said the unheated changing room felt risky for elderly bathers' heat-shock).
stated by 4 visitors · Jun 2025 – Jan 2026Bath temperature
The heated outdoor tub runs around 41C, though many reviewers describe the overall bath (especially indoors) as lukewarm/tepid (nurui), so expect a cool soak rather than a hot one.
stated by 3 visitors · Dec 2025 – Jun 2026The bath
What you’ll find
A small, remote mountain day-spa with genuine unheated flow-through indoor spring water (39C, pH 8.0, weakly alkaline and slippery) plus a heated outdoor tub, a weekend-only sauna, an on-site restaurant of inconsistent quality and hours, and a history of ownership changes and temporary closures.
Outdoor bath
✓ YesAn outdoor bath exists, but under the current owner its area has been cut to under half its former size and depth reduced about 20% (kerosene heating cost cited); reviewers also report ants and horseflies and unclear rust/mold debris in the tub.stated by 6 visitors · Jun 2025 – Jul 2026
Indoor baths
1One indoor bath.stated by 1 visitor · Oct 2025
Sauna
✓ YesA sauna exists but only operates weekends/holidays and shuts off as early as 17:00-18:00; one reviewer measured a low 76-78C and warned the resulting cold-plunge shock could be risky for elderly visitors.stated by 5 visitors · May 2025 – May 2026
Cold bath
✓ YesA cold plunge bath exists, but one reviewer warned that the sauna's unusually low temperature makes the cold shock uncomfortable and potentially unsafe for older visitors.stated by 2 visitors · Oct 2025 – Mar 2026
View
ForestThe facility sits surrounded by mountain forest, giving a quiet, natural setting.stated by 2 visitors · Aug 2025 – Oct 2025
Rest area
✓ YesA tatami rest room is available and spacious, but in cold months the changing room and rest room have had inadequate heating (one visitor said the unheated changing room felt risky for elderly bathers' heat-shock).stated by 4 visitors · Jun 2025 – Jan 2026
Restaurant
✓ YesAn on-site restaurant exists but is unreliable: it has been closed during off-season/weekday visits, seems to mainly run weekends, and reviews split between praise (ginger pork set, tanmen) and complaints of high prices and poor quality.stated by 9 visitors · May 2025 – Jul 2026
The water
Free-flowing (kakenagashi)
PartlyThe indoor bath is genuine flow-through spring water with no heating or added water, but the outdoor tub is separately heated (see 'heated' field), so only part of the facility is true kakenagashi.stated by 5 visitors · Jun 2025 – Jul 2026
Spring type
Weakly alkaline, slippery (nurunuru) textureThe spring is described as weakly alkaline with a soap-like slippery feel on the skin.stated by 1 visitor · Aug 2025
Source temperature
39°CThe spring source itself is measured at about 39C.stated by 3 visitors · Aug 2025 – Jun 2026
Bath temperature
41°CThe heated outdoor tub runs around 41C, though many reviewers describe the overall bath (especially indoors) as lukewarm/tepid (nurui), so expect a cool soak rather than a hot one.stated by 3 visitors · Dec 2025 – Jun 2026
pH
pH 8The water is reported to have a pH of 8.0.stated by 1 visitor · Oct 2025
Heated
PartialOne review describes the spring as entirely unheated and undiluted, but another clarifies this applies to the indoor bath only (39C, straight from source) while the outdoor tub is artificially heated to about 41C.stated by 2 visitors · Aug 2025 – Dec 2025
Water added
NoThe indoor bath water is not diluted with added water.stated by 2 visitors · Aug 2025 – Oct 2025
Guide
What visitors add
The water
Twelve distinct reviews describe slippery, skin-smoothing water (tsuru-tsuru/nuru-nuru); one reviewer cites pH 8.0 and another calls it weakly alkaline, feeling like soap on the skin. One notes a faint oil smell; another says there is no chlorine smell. The water is lukewarm overall: multiple reviewers describe it as mild/lukewarm, one measuring body-feel 39-40C and wishing it were hotter.
stated by 12 visitors · May 2025 – Jul 2026Water handling
The indoor bath is free-flowing source water without heating or dilution, at about 39C (reported by at least five distinct reviews, two citing a posted sign or thermometer at 39C); the outdoor bath is heated (one reviewer says kerosene-fired) to about 41-42C (three reviewers give temperatures in that range). Several reviewers note yunohana (mineral flakes) floating in the water; one reviewer clarifies the brown matter in the tub is yunohana, not dirt, while another (Jan 2026) found the floating black matter off-putting.
stated by 9 visitors · Jun 2025 – Jun 2026Outdoor bath & sauna
There is a small outdoor bath and a sauna with cold-water bath, but three distinct reviews say the outdoor bath was downsized under the current owner (to between one-third and half its former size), and three distinct reviews say the sauna runs only on weekends/holidays. Sauna shutdown time reports differ: 17:00 (Mar 2026 review) vs 18:00 (Oct 2025 review); one reviewer measured the sauna at only 76-78C and warns the cold bath feels punishing, with no outdoor rest chairs.
stated by 7 visitors · May 2025 – Mar 2026Price
Admission is 800 yen for 3 hours, reported by five distinct reviews (Nov 2025 - Jun 2026); one reviewer (May 2025) adds a 1,000-yen full-day option, and one notes there are no discounts. One reviewer bought coffee milk at reception for 180 yen.
stated by 6 visitors · May 2025 – Jun 2026Day-use visits
One reviewer (May 2025) says day-use bathing opens at 11:00. One reviewer (Oct 2025) complains closing time is earlier than nearby onsens and wishes it stayed open to 20:00-21:00. One reviewer (Jul 2026) reports hours were shortened after a bear was seen on the premises. One reviewer found food and sauna unavailable on an off-season weekday evening; another says the attached restaurant may run only on weekends/holidays and advises checking the website.
stated by 5 visitors · May 2025 – Jul 2026Staffing
The facility is staffed: three distinct reviews mention a reception desk (paying 800 yen at reception, buying drinks there, or friendly staff), and one notes staff gave safety advice about the slippery water. One reviewer notes the owner changed a few years ago.
stated by 3 visitors · May 2026 – Jul 2026Timing
When to go
| Day | Hours |
|---|---|
| Monday | 11:00–19:00 |
| Tuesday | 11:00–19:00 |
| Wednesday | Closed |
| Thursday | 11:00–19:00 |
| Friday | 11:00–19:00 |
| Saturday | 11:00–19:00 |
| Sunday | 11:00–19:00 |
Closed Wednesday.
Practical
Plan your visit
📍 2164 Matsuidamachi Kamimasuda, Annaka, Gunma 379-0211
🚃 Yokokawa station, 4.4 km
📞 +8127-329-6798
📋 Show at the counter: 上増田温泉 砦乃湯
Nearby
Other baths close by
Showa · 3.7★
Annaka · 3.8★
Annaka · 4.1★
Minakami · 3.2★
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