Kumagai Inn is a secluded onsen (hot spring) filled with carbonated spring water that is highly regarded by a select few. Located on the foot of the north west side of Mt. Sanbe, water in this secluded onsen has been springing up for approximately 200 years and has been popular all that time. The temperature of the onsen is only 37 degrees Celsius, which is a perfect temperature to relax in and enjoy. The carbonic acid bubbles in the onsen cling to your body and make your skin soft and smooth.