Kusatsu Onsen — photo: おにく · CC0 · Wikimedia Commons
.jpg){kind=link}
Kusatsu onsen: the yubatake, the acid water, and getting there
Kusatsu is the town people mean when they say they want a "real" onsen town. There is no railway station in it, it is about three to four hours from Tokyo, and the whole centre smells faintly of sulfur. What sets it apart is not the scenery. It is the water: hotter and more acidic than almost anywhere else in Japan, and in such quantity that the town has to cool it in the open street before anyone can bathe in it. That water is worth understanding before you go, because it behaves differently from the gentle baths most first-time visitors have tried.
What the numbers say
Our database holds 1,538 onsen towns. Kusatsu is recorded with sources between 44.9 and 94.5 °C, a pH of 1.0 to 2.2, and a flow of about 32,300 litres a minute. Each of those on its own is unusual. Together they are rare:
- Of the 596 towns with a pH on record, only 26 are more acidic than pH 3. Just one, Kawayu in Hokkaido at 0.8, has a lower recorded minimum than Kusatsu.
- Of the 1,167 towns with a source temperature, 51 reach 90 °C or more.
- Only five towns are both that hot and more acidic than pH 3: Kusatsu, Tamagawa in Akita, Osorezan in Aomori, Tateshina in Nagano and Kurinodake in Kagoshima. Of the five, Kusatsu is the one with a whole town built around it.
- Of the 425 towns with a flow figure, 357 record less than 1,000 litres a minute.
The town lists four water types: acidic, sulfur, chloride and sulfate. Only 57 of the 1,468 towns with a water type listed have four or more. Kusatsu is also big: 171 lodgings, room for about 12,500 guests a night, and some 3.27 million visitors a year. In our records, only the Nasu area in Tochigi, a whole group of villages counted together, reports more.
The yubatake, and why the water is cooled
The 湯畑 (yubatake), "hot water field", is the centre of town: a source pouring into a long run of wooden channels, steaming day and night, with a small waterfall at the end. The channels do two jobs. They let the water lose heat before it goes to the baths, and they collect 湯の花 (yu-no-hana), the pale mineral deposit that forms as it cools. Everything is built of wood because acid water eats through metal pipes.
Cooling matters because Kusatsu does not like to add cold water. Diluting the water weakens it, and local custom treats that as spoiling it. The traditional alternative is 湯もみ (yumomi): stirring the bath with long wooden boards, in rhythm and often with a song, until it is cool enough to enter. At the 熱乃湯 (Netsunoyu) hall beside the yubatake there are yumomi shows several times a day for a small fee, and at some of them visitors can try a board themselves. It is a performance now, but it began as a practical answer to the temperatures in the list above.
The yubatake is lit up after dark, and the evening is the best time to walk around it, after the day-trippers have gone. There is a free footbath at one corner.
Where to bathe
You do not need to rely on your inn's bath in Kusatsu. There are three kinds of place to try:
- Large public baths. The best known is 西の河原露天風呂 (Sainokawara rotenburo), a very large open-air pool at the top of a park ten or fifteen minutes' walk west of the yubatake, past streams of warm water running over the rocks. Others sit right by the yubatake. All charge an entry fee.
- Free communal baths. Kusatsu keeps a number of small 共同浴場 (kyōdō-yokujō) around town, maintained by the neighbourhoods. Some are open to visitors and free; others are for residents only and say so on the door. There is no staff, no soap and no towels. The water is often very hot. Be quick, be tidy, and follow the rules in our etiquette guide for unstaffed baths.
- Inn baths. Many inns will take day visitors in an afternoon window under the sign 日帰り入浴 (higaeri nyūyoku). See onsen without staying the night for how that works.
Different baths draw from different sources, so the temperature, the colour and the smell change as you go. Some are clear, some cloudy with yu-no-hana. The changing-room sign, the 温泉分析書 (onsen bunsekisho), names the source; our guide to reading the water sign explains it.
What the acid does, in practice
This is the part most guides skip. Water at pH 1 to 2 is closer to lemon juice than to tap water, and you will notice it.
- Cuts and scrapes sting. So does freshly shaved skin. Shave the night before, not just before you bathe.
- Keep it out of your eyes. Do not splash your face with bath water, and do not rub your eyes with wet hands. If it gets in, rinse with plain tap water.
- Take off jewellery and watches. Sulfur blackens silver, and acid water is hard on metal in general. Glasses frames and hair clips too.
- Keep soaks short. The baths are hot, and many are well above the 40 to 41 °C people are used to. A few minutes, out, cool down, back in, is the local rhythm.
- Rinse if your skin is sensitive. Many people leave the water on after the last bath, but if your skin feels dry or itchy, a rinse with plain water in the washing area is normal.
Your towel will come home smelling of sulfur for a while. Bring a plastic bag for it.
Getting there
Kusatsu is 148 km from Tokyo Station in a straight line, at about 1,200 metres up, and there are three common ways in:
- Train and bus. The JR limited express from Ueno to 長野原草津口 (Naganohara-Kusatsuguchi) takes about two and a half hours, and a bus from the station climbs to the Kusatsu bus terminal in roughly 25 minutes. Services are not frequent, so check the connection before you book. If you use a JR rail pass, check separately whether the bus leg is covered.
- Direct highway bus. Buses run from Tokyo Station and Shinjuku straight to Kusatsu in around four hours, with no change and room for luggage underneath. It is the simplest way if you have a big case.
- From Karuizawa. Karuizawa, on the Hokuriku Shinkansen, is 31 km away as the crow flies, and a direct bus takes a little over an hour. This is the route to use if you are coming from or going on to Nagano or Kanazawa.
The bus terminal is a short downhill walk from the yubatake, and most inns are within walking distance of one or the other. The town is on a slope; the walk back up from Sainokawara is the one that tires people.
By car, there is one warning. The high road over the mountains to Shiga Kōgen and Nagano, the route through the Shibu pass, is closed in the snow season, roughly from November to April. In winter, Kusatsu is reached from the Gunma side only. The volcano above the town, Kusatsu-Shirane, has also closed parts of that road in recent years when activity rose.
Kusatsu is not a day trip from Tokyo. Six or seven hours of travel for a few hours in town does not work. Plan at least one night, and two if you want time for more than one or two baths.
Kusatsu or Hakone?
This is the question most people are really asking. The honest answer is that they are different kinds of place.
Hakone is about 81 km from Tokyo Station, half the distance. It is a whole valley of separate spa areas with a mountain railway, a ropeway, a lake and, on a clear day, a view of Mount Fuji. It has five water types between its areas, but most of the water is mild; the one Hakone area with a source temperature in our records, Ubako, tops out at 63 °C. You spend part of every day moving around. Our Hakone guide covers it.
Kusatsu is one compact town on a hillside, with one strong kind of water at its heart and very little else to do except bathe, walk, eat and bathe again. You arrive, leave your bags, and do not need transport until you go home.
Choose Hakone for a first taste of onsen with sightseeing on the side, for a short trip, or if the people with you are not sure about very hot water. Choose Kusatsu if the bathing is the point, if you want to walk from bath to bath in a yukata, or if you have already done Hakone. In winter, Kusatsu has snow on the ground and a ski area above the town; Hakone rarely does.
Nearby, and very different
The mountains around Kusatsu hold water of completely different kinds, which makes a second night nearby worth considering.
Manza, about 8 km away across the mountain, is higher still, records 80 °C at source, lists acidic and sulfur springs, and has nine inns. It is the place for the milky white bath, and it is quieter.
Shima, about 17 km to the east but a long way round by road, is the opposite: a narrow valley town recorded at 43 to 82 °C with a pH of 7.7, listed as chloride and sulfate. Clear, neutral water. Going from Kusatsu to Shima is the easiest way to feel how much the chemistry of a bath changes what it is like to sit in.
Over the Shibu pass in Nagano, 19 km from Kusatsu, Shibu Onsen and the snow monkey park are close on the map but, in winter, a long way apart by road. Our Japanese Alps guide covers that side.
Things not to do
Do not try Kusatsu as a day trip from Tokyo.
Do not go straight into the hottest bath in town on your first soak. Start with a large public bath and work up.
Do not wear your silver ring, earrings or watch into the water.
Do not drive over the Shibu pass in winter, or assume your navigation app knows it is closed.
Do not use a residents-only communal bath because the door is open. Read the sign.
Do not assume tattoos are fine. The larger public baths and many inns still refuse them. A private bath is the reliable answer.
New to this? Start with how an onsen stay actually works and onsen etiquette. For other towns near Tokyo, see onsen near Tokyo. For more on the water, see sulfur onsen and reading the water sign. Tattooed, or shy? See going to an onsen with tattoos and baths you can have to yourself.