10. Wilderness Territory Resort

Location: Wisconsin Dells, Wis.
Website: wildernessresort.com

This park is advertised as the largest indoor water park in the U.S., and it is, with one caveat. The park sprawls across three buildings, so it is the largest in terms of total area. In the Wild WaterDome building, they have, what they call, a “Foil Tec” roof that allows guests to tan all year. You never have to venture outside again!