Hakone Kowakien Yunessan, a hot spring facility famous for hot spring baths in different flavors.

Yunessan admission is ¥2,900 for adults and ¥1,600 for kids. They also have a pure hot spring area where bathing suits are not allowed. That's ¥1,900 for adults. You can go to both areas for ¥4,100 if you don't mind your skin being deprived of too much natural skin oil and a prolonged increase in blood pressure. http://www.yunessun.com/enjoy/