I second the rec for the Grand Hotel. If you've ever watched "Somewhere in Time" with Christopher Reeve and Jane Seymour, you'll recognize the front drive. (The hotel in the movie was actually played by 2 hotels - this one, and the Hotel Del Coronado, here in San Diego).

If you're going through the UP of Michigan, stop at Grand Marais - the beach there is made almost entirely of onyx pebbles. Some gorgeous rocks. Dip your toes in Lake Superior. Don't be surprised if you have ice around the edges, even in July. Have fun!