Antony Gormley has scattered 31 human-like, iron sculptures on the rooftops of landmark buildings surrounding the Madison Square Park area in an exhibition called Event Horizon. Until August 15, you can play Where's Waldo with the eerie brown men overlooking New York (or if you're lazy here's a map of all the statues). Gormley's Event Horizon is definitely a lot more engaging than Olafur Eliasson's Waterfalls two years ago, especially when you look up and are surprised to see one of the mysterious men standing at the edge of a building.
There is a weekly photo competition hosted by Ace Hotel for the best photo taken of the sculptures. I really recommend checking out the amazing photos--and looking up when walking through NYC.