Castle Rock is an isolated sea stack of resistant Mackinac Breccia along a wave-cut cliff of ancient Glacial Lake Nipissing shoreline. Once a lookout of the Ojibwa, Castle Rock became a tourist attraction for early motorists traveling along U.S. 2 between St. Ignace and Sault Ste. Marie. Reached by a ramp and walkway, the outcrop that forms the shaft of the lookout tower rises 195.8 feet above the water level and 183 feet above the road level; it affords excellent views of Mackinac Island and Lake Huron. At the base of the lookout tower is a souvenir shop.