Taking a road trip from Boise, Idaho to Minneapolis! What should we see on the way?

Okay, well I am so excited, I got my plane tickets today to go home to Boise and see my family for a couple of days. Then, going to drive with my aunt from Boise to Minneapolis where her new life awaits and I am going to keep her company on the long drive. She has always wanted to see Mount Rushmore so we have that planned. Is there anything else along that general route to stop and see? Or what is there to see in Minneapolis? I will get to stay there and help her get settled for two days before returning back to Texas. What should I see in that great big city? What is a not to miss attraction or restaurant? I have no idea if I will ever get back there so I am looking at this as a once in a lifetime trip. I am so excited!!!