Fort Mackinac sits atop limestone cliffs near downtown. Built by the British in 1780, it's one of the best-preserved military forts in the country. Costumed interpreters and cannon and rifle firings (every half-hour) entertain the kids. Stop into the tearoom for a bite and million-dollar view of downtown and the Straits of Mackinac from the outdoor tables.
The fort admission price also allows you entry to five other museums in town along Market St, including the Dr Beaumont Museum (where the doctor performed his famous digestive tract experiments) and Benjamin Blacksmith Shop.