Aquapark Niigata

Aquapark Niigata is a really nice swimming pool facility in the western ward of Niigata City.  There is a large pool in a ring shape with a current that's fun for just floating around in (Aquapark has flotation devices you can use, or you can bring your own), and a smaller area with a water slide for kids.

Also, there is an area with heated water (like an onsen or sento) for relaxing in.  In addition to the pools, there are sento-style bathing areas attached to the changing rooms, saunas, massage services, a restaurant, and lounges on both floors.  For 500 yen (250 yen for children over 3 years old), it's a great place to relax on a cold, wet Niigata day.

Aquapark Niigata website: http://www.aquapark-niigata.jp/