Here's another plug for Minnesota. I live in Duluth (and it is a cool little city with beautiful views of Lake Superior and a lot of fun activities). But it is also a gateway to the North Shore, which is just gorgeous. I'm driving up to Grand Marais, MN in late autumn this year for 5 nights, and it is one of my favorites. It's evocative of a town in Maine, and is so lovely. And the drive up along the north shore of Lake Superior is breathtaking.
But I also love Minneapolis and St. Paul, and if you're looking for a fun big city vibe, they fit the bill. There are so many things to do there; beautiful lakes in the middle of the city, a striking downtown, gardens galore, museums like the American Swedish Institute, the Russian Museum of Art, the Minneapolis Institute, or just driving down Summit Avenue in St. Paul for a look at row after row of beautiful old mansions.
Or you can drive through some beautiful and quaint towns like Stillwater, MN or Lanesboro, which has been voted the pretties town in the US. Minnesota really does have so many wonderful places to visit.
And while you're in the north of Minnesota, you could easily drive over the bridge to Wisconsin, and head along the southern shore of Lake Superior to Bayfield, WI, which is known for its wonderful apple festival everywhere, and one of the most charming towns I've been it. It sits along the southern shore of Lake Superior. You could also take a trip to the Apostle Islands while you're there.