The B Loop Trail at Stony Brook Reservation in Boston, Massachusetts is a 3.5 mile loop hike that encompasses the entire reservation. The Stony Brook Reservation is a hidden gem near the Blue Hills Reservation, but is much less popular, so it's a great place to get outside near the city but without any crowds.
You can hop on the B Loop Trail really anywhere at Stony Brook, but the main parking areas are easiest to jump on the trail. The hike brings you through coniferous and deciduous forests, up to a lookout point above Turtle Pond, and another short hill 'lookout' are on the west side of the loop.
The trail itself is fairly flat with some ascents and descents along the way, but is not paved in any section. Dogs and biking are both allowed here.