From Shimosato, we drove a couple of hours to Kawayu Onsen nestled deep into the mountains, famous for its hot springs on the river banks. Visitors and locals alike would dig a small "bath" on the river bank where the boiling spring water bubbles up and also dig a narrow channel connecting it to the river to bring in the chilly river water to adjust the temperature. Since we had ample time today, we took a little side trip to the small quintessential town of Yunomine Onsen, where Japan's oldest hot springs called Tsubo-yu is located. We stayed at Kawayu Onsen Fujiya and indulged ourselves in their decadent full-course Japanese dinner and breakfast, not to mention multiple soaks in our in-room, open-air cedar onsen bath. If we must pick an ultimate Japanese experience, nothing beats the hot springs.