Start by track and basketball courts on Park Drive on sidewalk, run along Park Drive towards Boylston staying on sidewalk. Wraps all the way around the Back Bay Fens, passes gardens, ponds, salt marsh. One Loop is approx.2 miles, so you can do how ever many you like, based on what distance you would like ti run. It's a good mix of pavement and gravel/dirt, only a few small hills. Lovely scenery.
