If you go into the U.P., there is plenty to see. The drive on US 2 from St. Ignace to Engadine has some nice lake views and beach. Tahquamenon Falls is nice, and north of that is a little museum in a lighthouse. Then head to Munising and take the boat ride along the Pictured Rocks (make sure it's a calm, sunny day, and the sunset cruise has the best light). Head south to Fayette SP and walk around the old historic buildings where they smelted iron ore. Then drive to Palms Book SP and enjoy the clear, deep Big Spring where you can clearly see fish swimming around 40' below you.
Be sure to eat a pasty (like a pot pie) with gravy, and get some smoked fish if you like it; there are many places along the way. In Mackinaw City, look up the local bakery a block north of the main drag and buy some fresh cinnamon bread... but go early or it will be sold out.
