One day, we drove to Petoskey and Charlevoix. When we were ready to head back to Houghton Lake, we entered it in the Garmin and it led us to a road that ended at a lake and said "board the ferry". We laughed a lot and were a little confused at first, but then we saw the ferry across the lake and realized that it was for cars!
There wasn't much around, but we noticed this little restaurant next to the ferry stop so we went for some food and drinks and watched the ferry take cars back and forth across the water.
Eventually, we drove onto the ferry and road across. We had a nice chat with the operator and learned that we were on the Ironton Ferry. It was a fun adventure! Here is a link to an interesting article about it: http://www.mynorth.com/My-North/June-2008/Q-A-Ironton-Ferry-Captain/