Onsen waters gush out from the bottom of the Nagasasagawa River. The entire river is an onsen. The local people held back the river water to make a huge open-air bath out of it. People sit on riverbed stones, which are hot and help relieve their hemorrhoid problem. The open-air bath is free and open 24/7.
There is one more thing that is very appealing. Foreign tourists love to watch monkeys enjoying onsen. They take pictures, but that's about all. At Shiriyaki onsen, wild monkeys enjoy the onsen, so instead of just watching them, you can bathe with them. You should be very careful as they could be quite vicious.
You can be in the onsen with or without a bathing suit. There is no changing room, though. Shiriyaki Onsen closes on days with heavy rain, some days in the snowmelt season, and for other reasons that make the river water dangerous.
Origin of Shiriyaki Onsen
Way back in 1185, after losing a decisive battle, the fleeing Heike worriers came to the Kuni now part of Nakanojo area and discovered the onsen. They found the onsen waters very effective to heal and re-energize themselves. Soon, bathing in the river water onsen became their daily routine. The onsen water welling up from the bottom of the river felt ultra-hot on their buttocks, and they called it Shiriyaki Onsen.
On October 20, 1922, a well-known Japanese poet, Bokusui Wakayama (1885-1928) traveled the area from Kusatsu to Sawatari Onsen, crossing over the Kuresakatoge Pass, which offers a breathtaking view of autumn leaves. At 37 years old, Bokusui made a number of poems on the journey, and the local people built a monument with his poem inscribed on it along with his life-sized bronze statue. Every year on this day, they hold a festival dedicated to him.
As you bathe in the onsen, you can see the bubbles on the surface, by which you can tell the onsen water is gushing out from the bottom to the surface of the river. Approx. 56 degrees centigrade where it is hottest, you can move around the bath to find the place where the temperature is just right for you.
Shiriyaki Onsen is absolutely positively wild.