or a flat route with great views, run the Esplanade along both sides of the Charles River. The loop officially clocks in at about four and half miles, but the atmosphere changes from cityscape to greenery. From the Charles/MGH Red Line stop, run across the Longfellow Bridge, bearing left along the river. The halfway mark is the Boston University Bridge, which begins a new view of the Esplanade and Cambridge. Near Beacon Hill is lush flora. Run across the overpass near Community Boating to the reach the starting point. Canal