The popular Seibuen theme park, which lies just north of the Saitama-Tokyo border, is only 50 minutes from Shinjuku by train. Its outdoor pool, open during summer, covers a large area and features no less than four tubular water slides, the obligatory wave pool and plenty of shallow splashing spots for the little ones.
When you're taking a break from the water, you can fuel up on typical Japanese summer food, including yakisoba (fried noodles), somen (cold noodles) or okemori, a generous bowl filled with yakisoba, fried chicken and takoyaki (octopus dumplings).
A day at the pool costs ¥3,200 (primary school students and children aged 3 and older ¥2,200). Between August 9 and 17, tickets cost ¥3,500 (¥2,500). Tickets are now on sale and can be purchased online. (Aug 9-17 here)
Only open on weekends from June 28 to July 13 and September 1 to 15. Open daily from July 18 to August 31.