Great Adventure of Adventure Lagoon at Tokyo Summerland, is a 710-yard long pool, including water-splashing spots, water slides and more. (Courtesy of Tokyo Summerland)

Great Adventure of Adventure Lagoon at Tokyo Summerland, is a 710-yard long pool, including water-splashing spots, water slides and more. (Courtesy of Tokyo Summerland)

Water slides at Tokyo Summerland. (Courtesy of Tokyo Summerland)

JapanAQUA PARADISE PATIO (Saitama prefecture): year-round, 10 a.m.-9 p.m., closed Tue.; all-weathered indoor amusement pool has pools including water slider, water whirl, children’s pool, wave pool, and sauna baths; 15-minute drive from Hanazono I.C. on Kanetsu Express; 1,000 yen adults, 500 yen kids; 048-574-5000.