japan pools・ Swimming clothes must be made for swimming — no street clothes allowed in the pool. ・ Keep in mind that in much of Japan, tattoos may prevent you from gaining admission. There are tattoo cover stickers available.Rainbow 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