Kusatsu has the largest natural spring water flow of any spa in Japan. It is popular among tourists, attracting 2.7 million visitors annually. Waters are extremely hot and strongly acidic. For centuries, people have traveled to Kusatsu to benefit from the water's medicinal properties. The town which developed around the spa, includes numerous inns for long-term recuperation. Even today, people still follow the rules of jikan-yu, a unique bathing method introduced in the Edo Period. Our story focuses on the spa water, natural surroundings and people of Kusatsu.