japan poolsAn overnht stay at an onsen ryokan, in particular, is a hhly recommended experience to any visitor of Japan. Basics. How to take a bath. Types of baths. Types of water. Best Onsen inRainbow Pool at Showa Kinen Park. A hit with families every summer, Rainbow Pool is the bgest waterpark in the Tokyo Metropolitan area, featuring 9 pools covering a staggering 63,000 square meters. With a lazy