Near North Andover, the 3,500 acre Harold Parker State Forest has a nice section of the Bay Circuit Trail rolling hikers through maple and oak forest, low lying swampy areas, and rock outcropings. This forest can be quite moist and lush during the summer producing a bumper crop of mosquitos - so bring lots of repellant.
To reach the forest from Boston, follow SR93 north to exit 41, follow 125 north (toward Andover), for about 2.5 miles to the State Police Barracks (on right). Turn right on Harold Parker Road for 1.2 miles to Jenkins Road Turn left on Jenkins for 1 mile and then right on Middleton for 1.2 miles and look for Headquarters parking area on the left.
Overall, Bay Circuit Trail is the 15th most popular hiking trail of all 36 hikes in Massachusetts.