Seibu Amusement park will open their NIGHT POOL from July 15th on Fridays, Saturdays and Sundays until 9pm in July and from the 15th to the 19th and on Fridays in August. Cost: Day pass for adults and children over 15 is 3,000 yen. For kindergarten and primary school aged children and people over 60 the price is 1800 yen for a day pass. Children under 2 are free. Summer water park at Seibu Facilities: 4 pools (1 is massive) which include one 30 cm water depth pool that children in nappies / diapers ARE allowed into. Children over 3 are allowed to zorb on water with a parent. They have an “Hello Kitty Water Park” which is a separate water play area. Access: The summer water park at Seibu Amusement park is a 5 minute walk from Seibu Tamako Line Seibu Yuenchi Station and Seibu Line Seibuen Station. Parking for 1200 cars, costs 1,300 yen for one day until July 31st, 1,500 yen per day from August 1st. Sat nav/ GPS: phone number 042-922-1371 Other: Seibu Pools, in my experience to date, are the most expensive in Saitama.  The amusement park launches fireworks during the summer and the park also has a seasonal beer garden. They have a night pool from July 15th. URL: http://www.seibuen-yuuenchi.jp/guide/pool/index.html