We got a ferry ride to Mackinac Island & combined it with a carriage ride around the island. It was a good overall to see a lot. There are 2 ferry operators, Shepler's & Starline. We took Starline but there was some delays. I think Shepler has more ferry service.
For an extra fee you can tour the butterfly garden. We didn't.
Arch Rock
You can tour the fort for an extra fee. We didn't.