This small section of the Bay Circuit Trail is a 4.3 mile out-and-back trail that goes along the Sudbury Reservoir in Southborough, MA. The hike is mostly flat, with some uphill sections closer to the northern terminus. In autumn, this is one of the best hikes in eastern Massachusetts to see foliage along the water and in a fairly secluded area. This trail gets traffic, mostly in the early mornings and evenings, but is not a very popular spot.
The trail is mostly flat until you reach the northern section near Parmenter Road where the trail shoots uphill before becoming flat again. Biking is allowed here as well as dog walking, on-leash.