Know Before You Go
The ferries. Mackinac Island boats leave from the docks right downtown, roughly every half hour in season, about twenty minutes across. You do not need to leave from Mackinaw City; St. Ignace boards calmer and parks easier.
The season. Mid-May through October is the show; things wind down hard after the island closes up. Winter St. Ignace is beautiful and very, very quiet — check hours on everything.
The bridge. Crossing the Mackinac Bridge costs a few dollars per car, takes about seven minutes, and if you're nervous about bridges, they will literally drive your car across for you. Really. It's a free service; look up the Bridge Authority's driver assistance before you go.
The fudge. Yes, it's everywhere. Locals call tourists "fudgies" and buy it anyway.
The chains. If the kids stage a mutiny, town has a McDonald's, Burger King, Taco Bell, and Subway. You didn't cross the bridge for them, but they're there.
Laundry & parking. Doing the trip out of a camper, or heading to the island for a few days? Bayside Coin Laundry on State Street is open 6am to midnight daily — self-serve machines, wash-and-fold drop-off, and ferry parking (day, overnight, and seasonal) two minutes from the docks.