Fort St. Joseph is the island's headline sight. The British built it after leaving Mackinac in the 1790s, and forces from here helped capture Mackinac early in the War of 1812. The fort was later burned and abandoned, leaving ruins, earthworks, and a large, quiet landscape at the south end of the island.
Parks Canada keeps the site low-key, which suits it. Walk the trails, look across the water toward the old borderlands of the upper Great Lakes, and give the visitor centre enough time to explain why this remote place once mattered.