The river itself is a hot spring!
Enjoy playing in the river and bathing at the same time.
The hot spring naturally wells up from the bottom of Nagazasazawa-gawa River flowing from Shigakogen Highlands (Nagano) and Mt. Kusatsu-Shirane (Gunma). Dig anywhere on the riverbed and hot water might well up. The flowing river itself is a hot spring. A huge open-air bath made by constructing a dam in the river is Shiriyaki Onsen that is also called Kawa-no-yu (river hot spring.) The name literally means "buttocks burning hot springs". It is said that people sat down on the riverbed and cured their hemorrhoids on stones warmed by hot water. They say the water is good for rheumatism, skin diseases, feminine problems and hypertension in addition to hemorrhoids. The water contains calcium, sodium, sulfate salts and chlorides.
Being in the midst nature, the hot spring is available anytime for free, but the water level is too high to soak especially after heavy rain and snow melting season. There is no changing room and some people soak wearing swimsuits while others are naked. This is a true natural bath in a rustic atmosphere.
The onsen is only 10 km from Kusatsu Onsen that is a major onsen resort. There are three onsen accommodations in Shiriyaki Onsen. This is a place to casually enjoy a hot spring that is not known to many people.
Address: Iriyama, Nakanojo-machi, Agatsuma-gun, Gumma
Phone: 0279-95-3111 (Nakanojo Town Office Kuni Branch)
Directions: [Rail] 30 minutes by bus for Hanashiki Onsen from JR Naganohara kusatsuguchi Station (2 hours from Tokyo Station) and 10 minutes on foot
[Car] 1 hour from Shibukawa-Ikaho Interchange on the Kan-Etsu Expressway