From behind a parapet on the tower of Litchfield Villa, the Italianate mansion that marks the western edge of Brooklyn’s Prospect Park, I was barely able to make out — over treetops and tall buildings — a glint of Gowanus Bay, roughly two miles away. Edwin Litchfield, the railroad and real-estate tycoon who built this house in 1857, would have had no trouble seeing the bay and much of his landholdings out of a second-floor window, from the hilly and largely treeless farmland outside his front door all the way down to the grassy banks of Gowanus Creek, which by the…