Quick FactsOverview
About Sainokawara Rotenburo
Sainokawara Rotenburo, Japan is a large public outdoor hot spring bath in Sainokawara Park, in the Kusatsu onsen resort of Agatsuma District, Gunma Prefecture. At 500 square metres it is one of the largest rotenburo in Japan and can comfortably accommodate up to 100 bathers at once. The bath is approximately 12 to 15 minutes on foot from the Yubatake hot water field in the centre of Kusatsu, along a stone-paved promenade through the park that passes a small Shinto shrine, Jizo statues, stone lanterns, and a riverside walking path.
The water is an acidic chloride-sulphate spring fed by the Bandai hot water source. It is highly acidic, consistent with Kusatsu's volcanic waters, and the bath sits in a forested park setting that provides changing foliage views through the year. The pools are shallow. There are no showers; visitors pour water over themselves at the entrance before entering. No soap or shampoo is provided. The facility is open year-round on all days. Gender-separated pools serve men and women separately on most days. On Friday evenings, the men's bath opens for mixed bathing; swimwear is permitted during this session and rental swimwear is available. A free foot bath is also located in Sainokawara Park.
Location & Access
Getting to Sainokawara Rotenburo
Sainokawara Rotenburo is in Sainokawara Park, Kusatsu, Agatsuma District, Gunma Prefecture, at the address 521-3 Kusatsu, Agatsuma District, Gunma 377-1711. It is approximately 12 to 15 minutes on foot from the Yubatake in the town centre, following the stone-paved promenade north-west through the park. Access to Kusatsu itself follows the same routes as Kusatsu Onsen town: from Tokyo, take a direct highway bus from Shinjuku Bus Terminal (approximately three and a half to four hours) or take the Hokuriku Shinkansen to Takasaki Station and then a bus to Kusatsu (approximately one and a half hours). The Naganohara-Kusatsuguchi Station on the JR Agatsuma Line is the nearest rail station, with a JR Bus connection to Kusatsu Bus Terminal in approximately 25 minutes.
Sainokawara Rotenburo is open every day. Summer hours (April through November) run 07:00 to 20:00 with last entry at 19:30. Winter hours (December through March) run 09:00 to 20:00 with last entry at 19:30. Admission is 800 yen for adults and 400 yen for children aged 3 to 12. There are no showers; a splash-water station at the entrance is used for pre-bath rinsing. Lockers are available for 100 yen. On Friday evenings, the men's bath opens for mixed bathing from 17:30 to 20:00; swimwear is permitted and swimsuit rental is available (free for men, 400 yen for women). The women's bath remains women-only at all times.
Suitability & Accessibility
Who Sainokawara Rotenburo Suits
Sainokawara Rotenburo suits visitors to Kusatsu Onsen who want the area's most dramatic outdoor bathing experience. The sheer scale of the 500-square-metre pool, the forested park setting, and the open sky make it a different experience from the indoor baths in town. It is the most popular outdoor bathing destination in Kusatsu and is well-suited to visitors who want to combine a walk through Sainokawara Park with a soak, particularly in autumn for the foliage or in winter for snow-surrounded outdoor bathing.
Couples, solo visitors, and groups are all accommodated. The Friday evening mixed bathing session, with swimwear permitted, makes it one of the more accessible communal bathing experiences for visitors who are less comfortable with traditional nude onsen. Families with children aged 3 and above can use the facility; the pools are shallow, making the water depth manageable.
The high acidity of the water (consistent with Kusatsu's volcanic pH 1.7 to 2.1 range) is more chemically active than most onsen in Japan. Visitors with sensitive skin or skin conditions should take this into account and rinse promptly after bathing. No soap or shower is available at this facility; it is best suited to those who do not need to wash hair or use products. Wheelchair accessibility is not specifically documented; the park paths are stone-paved and the bath area involves steps.
Safety & Etiquette
Sainokawara Rotenburo Safety Tips
Sainokawara Rotenburo is generally safe as a managed public facility in a well-visited park, but the highly acidic volcanic water and the outdoor mountain setting require awareness that is not needed at most urban or hotel onsens.
The Kusatsu spring water at this facility is highly acidic, with the same pH 1.7 to 2.1 range as the Yubatake source. Do not submerge the face or eyes in the water. Rinse skin and hair thoroughly after bathing. The acidity can cause irritation on sensitive skin or around open wounds; exit and rinse immediately if this occurs. People with heart conditions, hypertension, or active skin conditions should consult a doctor before bathing. Limit soaking to 10 to 15 minutes and rest between sessions; the outdoor setting and cold air in winter increase the contrast with the hot water and can intensify the physiological effects.
There are no showers at the facility; pour water over yourself at the entrance splash station before entering any pool. Do not take cameras or smartphones into the bathing area. The pools are shallow but the rocky base can be slippery; move carefully and avoid running. On Friday evenings during mixed bathing, swimwear is required; the women's bath remains gender-separated at all times. In winter, the path through Sainokawara Park can be icy; wear appropriate footwear for the walk from the town centre. The changing rooms are unheated and can be very cold in winter; have warm layers ready to put on immediately after bathing.
