Photo by Aspere, via Wikimedia Commons (CC0)
🇯🇵 Japan · Gunma
♨ Temperature
95°C
⛰ Altitude
1156 m
⚗ pH
2.1
💧 TDS
1580 mg/L
🌊 Flow rate
32 L/s
📅 Established
720
✓ Verified on 2026-07-22
Kusatsu Onsen sits at over 1,100 metres in the Gunma highlands and has been celebrated in Japanese literature and poetry for more than 1,300 years. Its defining feature is the Yubatake — a wooden grid of channels in the town square where steaming mineral water flows at 95°C before being cooled for bathing. The water is among the most acidic of any major Japanese onsen, with a pH around 2.1, produced by volcanic hydrothermal activity beneath Mount Shirane. Kusatsu's traditional bathing method, jikan-yu, involves immersing in very hot water for precisely three minutes — a practice maintained in several communal bathhouses. The town's high elevation means snow-covered streets in winter, making the contrast of outdoor hot baths against snowfall one of Japan's classic seasonal experiences.
| Sulphur | 56 mg/L |
| Chloride | 512 mg/L |
| Sulphate | 780 mg/L |
| Aluminium | 73 mg/L |
Kusatsu's springs are documented in the Nihon Shoki chronicles of 720 AD. The town's communal bathing culture evolved over centuries into a system of public bathhouses called sotoyu, each maintained by local neighbourhood associations.
Kusatsu is the subject of numerous Japanese folk songs, most famously the Kusatsu Bushi melody sung by bathers for generations. The tradition of yumomi — cooling the water by rhythmically stirring with large wooden paddles — has been performed as public entertainment at the Netsu-no-Yu bathhouse since the Meiji era.
The Yubatake flow and temperature are monitored continuously by Kusatsu Town as part of a broader volcanic observation programme linked to Mount Shirane's activity. Spring output has remained stable for decades, and the town limits commercial drilling to protect the natural aquifer.
Phone+81 279-88-0800
Websitewww.kusatsu-onsen.ne.jp/foreign/en/
AddressKusatsu, Agatsuma District, Gunma 377-1711, Japan