There is a water park in the Depot Renaissance (converted Courtyard) / Residence Inn right downtown, the neighborhood is very cool although there is a gentleman's club one block away, so beware, if you stay on the property it is a converted train station (Hiawatha Flyers) that is really great with a lot of history and memorabilia. Should be fairly cheap on points on the Residence Inn half. And of course there is the built in water park.

I really enjoyed my stay there.