The natural hot spring water that flows through the famous onsen town of Kusatsu (Gunma Prefecture) comes from deep within the earth and, as a result (and as you would expect), is very, very hot. Around 50 to 90 degrees celsius to be exact. That’s of course way too hot for anyone to soak in, so how is the water cooled? By adding cold water? While that is an intuitive solution, it would dilute the mineral content of the hot spring, and therefore, diminish its healing benefits (such as relieving muscle, joint pain and fatigue).
So, the technique used to achieve a comfortable bathing temperature is called yumomi, and in fact, dates back to the Edo Period (1603 – 1868). The process (more so, ceremony) involves stirring the water with large, wooden boards measuring about 1.8 meters long, whiffing in air to bring the temperature down. Held six times a day (three in the morning and another three in the afternoon) near the heart of the town in a charming two-storey wooden building called Netsunoyu, you can witness the Yumomi ceremony for a well-worth fee of 700 yen per adult.
It is quite a mesmerizing performance where two lines of women positioned on either side of a bath use the wooden boards to stir the piping hot water rhythmically, while singing a traditional folk song. The ceremony really feels like a window into the past. It’s the preservation of traditions such as this one that make Kusatsu Onsen so special, reminding us necessity is the mother of invention and that sometimes, the most simple method is the best (also, teamwork makes the dream work)!
Pro tip: If you want to catch one of these Yumomi ceremonies (which you should!), get in line early. The first performance of the day seems to be the most popular, and tickets can only be purchased 30 minutes in advance. Netsunoyu offers seating on two levels, which is given on a first come, first served basis. You may be tempted to sit on the second floor for better viewing, but there is one distinct advantage to the lower-level seating. Close proximity to the stage means you have a greater chance of being picked as a volunteer after the performance to experience stirring the water yourself.
Netsunoya: https://www.kusatsu-onsen.ne.jp/netsunoyu/index.html#section01
Google Maps: https://maps.app.goo.gl/WdkzP49HJpNhpZuW7