My wife and I did a two week tour of several cities in Minnesota, including Grand Marais, Duluth & Hibbing. We were up there to escape the Florida heat and didn't really know what we were going to do, but turned out to have a really great vacation. Please see my other posts regarding lodging, meals, etc. if you are interested in a similar trip.
Spent a couple of days in Hibbing. The open mine pit was interesting to see. Pretty much a big ugly hole in the ground, but a necessary evil if you want to have things made from metal. It was interesting to watch the equipment work for a little while. I think they have guides there at certain times, but I don't think you'd spend more than 30 minutes or so.
The 'old' Hibbing was nice enough to walk around or ride your bike through, but nothing terribly exciting. It was more interesting to visit the Hibbing museum to learn about Hibbing's stories.