大滝乃湯

Ōtaki no Yu is a celebrated day-use public bathhouse in Kusatsu Onsen, Gunma — Japan's most famous hot-spring resort. It is one of the town's "three baths" (Kusatsu Santo).

The water

The baths are fed by the Niekawa source (煮川源泉), an acidic sulphur hot spring with a pH of about 2.1. The water is strongly acidic, high-temperature and rich in sulphur, aluminium, sulfate and chloride, carrying hot-spring flowers (yunohana) and a faint milky turbidity. This source is piped exclusively to Ōtaki no Yu and the nearby Niekawa bath, and is prized as some of the freshest, least-oxidised water in Kusatsu.

Awase-yu baths

The signature feature is the traditional Kusatsu awase-yu method: hot spring water flows in sequence through a row of pools, cooling naturally to bathing temperature without dilution. Bathers progress from milder to progressively hotter pools to acclimatise the body.

• Large indoor public bath (大浴場)
• Outdoor bath with a large hot-spring waterfall
• Graduated awase-yu pools (a women-only awase-yu was added in 2012)
• Sauna kept at roughly 92–96°C
• Private rental baths, lounge and dining

Visiting

Open 09:00–21:00 (last entry 20:00). Set in the heart of Kusatsu, an easy walk from the steaming Yubatake hot-water field at the centre of town.