In the center of a fountain in a small park at the apex of West Broadway and Greenwich Street, in front of 7 World Trade Center.
The sculpture resembles one of those balloon figures a clown or magician might create to entertain children, except huge and colored candy apple red (which is exactly what the artist had in mind, according to the Silverstein Properties office). This is apparently one of Koons' specialties: according to his website, there are five of this same design in different colors, as well as various others using the same technique.
The fountain itself is dedicated to the memory of those who survived 9/11. The Silverstein Family Park is within Ground Zero, part of the original footprint of 7 WTC, one of the buildings destroyed on 9/11, and the first to be rebuilt.