Madison Square Park's newest work of public art utilizes one of the oldest photographic devices around: the camera obscura (the principle behind pinhole cameras), which inverts images and lends them a dreamy blur as it projects them. NYC artists Sandra Gibson and Luis Recoder's Topsy Turvy, which turns the Flatiron Building on its head, is a giant, cylindrical camera obscura that also warps these projections because of its shape. Three to five people can enter the walk-in installation at a time. All ages.