Curiously (apart from changing planes) the Twin Cities of Minneapolis/St.Paul is the only part of the US we've been to. We had a friend doing a year's secondment at the University, and we stayed with her. The cities are basically on opposite sides of the Mississippi, which becomes un-navigable by big boats only a little way further north. Nice places - great wide streets, and downtown Minneapolis has covered walkways at first floor height so you move from building to building without going outside (snow measured in feet during the winter, apparently!)