We've all seen them but might have been too scared to enter: the house on the hill with its boarded-up windows; the darkened factory on the outskirts of town; the old amusement park with its rickety skeleton of a rollercoaster. These are the ruins of America, filled with the echoes of the voices and footfalls of our grandparents, or their parents, or our own youth. Where once these structures were teeming with lifecommuters, workers, vacationersnow...