Rock Circuit Trail (Pinnacle Rock Extension) is a hiking trail in Middlesex County, Massachusetts. It is within Middlesex Fells Reservation. It is 422 feet long and begins at 191 feet altitude. Traveling the entire trail is 0.2 miles with a total elevation gain of 72 feet. The trail ends near Pinnacle Rock (elevation 249 feet). There are also wetlands and a viewpoint near the end of the trail.