I dropped a 100-yen coin into the foot bath at the yubatake by accident. It slipped out of my hand, sank to the bottom of the trough, and I assumed it was gone. I came back two hours later, intending to fish it out with my geta strap, and the coin was half-dissolved. The surface had gone dark and rough, the rim was pitted, and the design was starting to disappear. The yubatake water is genuinely acidic. It does that to metal. It also does that to your skin, in the best possible way.
Kusatsu is a small mountain town in Gunma Prefecture, about three hours from Tokyo by train and bus. It has been ranked the number one onsen town in Japan by domestic travel surveys for over a decade running. The ranking is not a marketing stunt. Once you have soaked in the water here, the case is obvious. The water is hot, sulphur-rich, slightly acidic, and noticeably softer on the skin than almost anywhere else in the country.
The yubatake: the heart of the town
The yubatake, literally "hot water field," sits at the centre of Kusatsu. It is a tiered hot spring source about 500 square metres in size, with the source water bubbling up from underground, cascading through a series of wooden troughs and shallow pools, and then being piped to the public baths and ryokan across town. Steam rises from it constantly. At night it is lit, and the effect is genuinely otherworldly.
The yubatake is not for bathing. It is too hot, and it is the source, not a soak. What you do at the yubatake is walk around it, watch the water, drink the free hot spring water from the public tap at the side, and soak your feet in the foot bath that runs along the edge. The foot bath is free, open 24 hours, and the single best free thing in any onsen town in Japan.
The water here is the same water that fills every bath in Kusatsu. The temperature at the source is about 90 degrees Celsius, and it has to be cooled to between 40 and 50 degrees before it is safe to soak in. That cooling is part of the town's bathing ritual.
Yumomi: the cooling ritual
Before modern plumbing, the only way to cool the source water was to stir it. Yumomi is the traditional Kusatsu method for doing this: women standing on a wooden platform above a shallow trough, stirring the hot water with long wooden paddles while singing a local folk song. The stirring cools the water by about two degrees and oxygenates it. The singing is not incidental. It coordinates the rhythm of the paddles and turns the chore into a public performance.
Yumomi performances happen several times a day at the Yumomi stage, which is right next to the yubatake. The schedule is posted outside, and the times vary by season. It runs about 20 minutes and is well worth stopping for, even if you do not bathe in town. The song has been the same for centuries, and the performers are usually local women who have done it for decades.
The water itself: what makes Kusatsu different
Kusatsu water is classified as a acidic sulphur spring, with a pH around 2 to 3. For comparison, lemon juice is about pH 2. That is why the coin dissolved. It is also why the water feels the way it does on your skin.
Kusatsu water is so acidic it dissolves coins. It also makes your skin feel incredible for about 24 hours after a soak. The acidic water softens the outer layer of dead skin, opens the pores, and leaves a noticeable smoothness that lasts most of the next day. I noticed it the first time and have checked since. It is real. It is also why Kusatsu water is reputed to help with skin conditions, and why the town has been a destination for that reason for centuries.
There is a tradeoff. The acidity means that long soaks can dry the skin out, particularly in winter, and the sulphur smell lingers in your hair and on your towel until you wash it. People who are sensitive to strong mineral water should keep the first bath short, around ten minutes, and work up from there.
The public baths in town
Kusatsu has two major public bath complexes in the town centre, and a series of smaller neighbourhood facilities.
- Yubatake no Yu. A modern, hotel-style facility with both indoor and outdoor pools, a sauna, and a rest area. It is the easiest entry point for visitors and is usually the first bath people try. Open until late, well-maintained, and a good first taste of the Kusatsu water.
- Sainokawara Rotenburo. A large outdoor bath in a river valley about 20 minutes' walk from the town centre. The setting is exceptional, with the bath carved into the rocky riverbank. The water is the same source but the experience is more rustic. Worth the walk in good weather.
- Goza no Yu. A traditional wooden bath near the yubatake. Small, atmospheric, and a good example of what an Edo-period Kusatsu bathhouse looked like.
Each bath charges a separate admission fee, usually 600 to 1,000 yen for adults. There is no combined pass like Kinosaki's. Most visitors pick two and spend the rest of their time at the ryokan bath.
Tattoo policy: mixed, mostly restricted
Here is the honest version. Most public baths in Kusatsu restrict visible tattoos, and the policy is more strictly enforced than at smaller towns. The Yubatake no Yu and Sainokawara Rotenburo both have signs at the entrance asking guests with visible tattoos to cover them. The smaller Goza no Yu is similarly strict.
The exception is ryokan. A meaningful number of Kusatsu's ryokan either allow tattoos in their in-house baths or, more commonly, offer private baths (kashikiri buro) that you can reserve by the hour. If you have visible ink and you want to soak in Kusatsu, the path is to book a ryokan and ask about their private bath option at the time of reservation. Most will say yes.
For the public baths, cover up with the same waterproof flesh-toned tape I recommend on the tattoo-friendly guide. It works in Kusatsu water just as it does elsewhere. Do not expect to walk into the public baths with a full sleeve uncovered. The policy is institutional, and arguing at the counter does not change it.
The other practical option is to book a day-use plan at one of the tattoo-friendly ryokan in town. Several offer daytime access to their private baths for non-staying guests, which is the cleanest workaround. The ryokan pages below are where I start.
What to book
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If you want to make Kusatsu the centrepiece of a trip and let someone else handle the logistics, a guided day tour from Tokyo is the easiest entry. Search Kusatsu onsen tours on Viator for current options that pair the town with a stop at a nearby attraction. Most include transport from Tokyo and either a ryokan lunch or a soak at a partnered facility.If you want to stay overnight in town, book directly with the ryokan rather than through a third party. Most ryokan in Kusatsu have English-language websites now, and direct booking gets you clearer answers on the tattoo question and the private bath availability than a generic booking platform will.
When to visit
Kusatsu is open year-round, but the peak seasons are summer (July to August) and winter (December to February). Summer is when the town is busiest with domestic travellers escaping city heat. Winter is when the steam looks most dramatic against the cold air, and the snow makes the yubatake look like something from a woodblock print.
I prefer the shoulder seasons. Late May and late October give you the bath without the crowds, and the mountain foliage in late October is excellent. The town is small enough that off-season crowds still feel comfortable, but you avoid the booking pressure of peak dates.
Getting there
From Tokyo, take the JR Takasaki Line limited express to Naganohara-Kusatsuguchi Station, about 1 hour 20 minutes. From there, a local bus runs to the Kusatsu Onsen bus terminal in about 25 minutes. Total door-to-door from central Tokyo is around 3 hours. There are also direct buses from Shinjuku that take about 4 hours, useful if you have luggage.
Within the town, everything is walkable. The yubatake, the public baths, the ryokan, and the restaurant strip are all within a 15-minute walk of each other. You will not need a car or a taxi.
A final word
Kusatsu earns its reputation. The water is genuinely different from anywhere else I have soaked in Japan. The town is small enough to feel like a village, the yubatake is unlike anything else you will see on a trip to Japan, and the surrounding mountains give the place a quiet that is hard to find closer to Tokyo. If you have the time for one major onsen town beyond Hakone, this is the one I would pick. Even with the tattoo friction at the public baths, the ryokan private bath option solves the problem completely.