A giant bath complex next to Tsutenkaku Tower in Shinsekai. The 'Europe zone' (Rome, Greece, Mediterranean) and 'Asia zone' (Bali, Persia) swap between men and women each month. There's also a swimsuit pool, stone saunas and hotel floors. Open 24 hours, so it doubles as a place to stay after the last train. Tattoos OK if covered with a sticker.
The heart of Kusatsu, where 4,000 litres a minute cascade down wooden channels. The Yukemuri-tei pavilion beside it is a free 24-hour foot bath, lit up at night. Start your visit here.
A large day-spa 12 minutes from Hakone-Yumoto Station, open 23 hours (10 am to 9 am). A 17-metre rooftop open-air bath, garden waterfalls and private baths. Overnight stays cost extra.
A natural open-air bath on the Asahi River gravel bed right below Yubara Dam, where water bubbles up through the riverbed itself — ranked the 'western grand champion' of Japan's rotenburo. Three pools at different temperatures; mixed, free and open 24 hours. Only a simple changing hut, so women are advised to wear a bathing garment (sold and rented in town). Closed Wednesday mornings for cleaning. Photography strictly forbidden.
The communal bath at the heart of Nuruyu Onsen in Kuroishi, Aomori, a spa with more than 400 years of history. It is ringed by 'kyakusha' — simple self-catering cure lodgings with no baths of their own, whose guests all walk over here — a form of spa life now rare even in Tōhoku. The bathroom is as roomy as a sentō, with 100% source water (sodium chloride-sulphate) cooled by a special method without dilution and split into hot and lukewarm tubs. Adults pay ¥350; open long hours from 05:00 to 22:00 (last entry 21:30), daily (occasional closures in April and November). No soap provided. Kokeshi-doll workshops and the Tsugaru Kokeshi Museum are nearby. About 25 minutes by bus from Kuroishi Station.
Tsuetate Onsen, where inns line both banks of the Tsuetate River on the Kumamoto–Ōita border, claims 1,800 years of history as the bath water of the infant Emperor Ōjin. Moto-yu is the communal bath said to be its origin: a single half-open tub carved into the rock face beside the riverside promenade — mixed, free and open 24 hours, nothing more. The sodium-chloride water, cooled from a 98°C source, leaves the skin soft. Changing space is basic and screening minimal, so many people wear bathing garments or a wrapped towel; early morning or night is the best time. Combine it with a wander through the 'sedoya' back alleys and, in May–June, the 3,500 carp streamers strung across the river. About 50 minutes by bus from Hita Station.
A stay-as-long-as-you-like hot spring resort among the fields of Takatsuki, in northern Nagahama near the top of Lake Biwa. The chloride spring pumped from 1,500 m underground is gentle on the skin and keeps you warm, earning it the nickname 'beautiful-skin water', enjoyed in indoor and open-air baths. The men's side has a high-temperature sauna and bubble bath, the women's an herbal mist sauna and jet bath, each with a cold plunge and outdoor cooling area. Inside are a lounge with co-working space, nap 'nest rooms', a restaurant and even lodging, and the complex is open around the clock (bathing suspended during cleaning). The basic bathing course without loungewear costs ¥900 for adults on weekdays and ¥1,200 on weekends and holidays (children ¥500/¥700, valid 6:00–24:00); the relaxed course with loungewear and towels is ¥1,600/¥1,800, with a surcharge from midnight to 6 am. Closed the second and fourth Wednesdays. About 1.9 km from JR Takatsuki Station or 5 minutes by taxi from Kinomoto Station, and close to the Kinomoto IC on the Hokuriku Expressway – a good base for the Kohoku Kannon temples, Nagahama and Lake Yogo.