Shimosuwa is a hot, hot spring. There is a sign by the entrance telling the daily temperatures of the main bath, the outdoor bath, and the showers. Even the showers here are spring water. Thankfully they have a municipal cold water wash basin for rinsing off and cooling off. However, that water is so cold! This is an onsen village for people who like it hot. When I was there a young 5-year-old boy could not enter the bath because it was too hot. He dipped his feet in to the main indoor bath a few times but was, nope, not getting in that! On the day I visited the bath was 44.5 at the hottest. Thankfully, the temperature of the outdoor bath was more reasonable and quite relaxing. Ko-yu is the biggest and has the most diverse selection baths of the 3 bathhouses on the route.