The Freedom Tower in the World Trade Center complex in New York City.
Workers and visitors to the new One World Trade Center building are leaving their personal marks on the concrete and steel of the fast-rising tower. Graffiti tributes to the victims of the Sept. 11 terrorist attacks have popped up on beams, walls, and stairwells of the new structure. Presumably once it is finished the results will vanish. See some of the heartfelt temporary art in this video: