When the Citigroup Center (formerly the Citicorp Center, formerly the Citibank Center) :) was first built, St. Peter's church - located on that corner - refused to sell their land to the developer. In a creative effort for compromise, the church agreed to sell the air space over their property, and the Citigroup tower was redesigned to stand atop pillars and was suspended over a rebuilt church. This invented the concept of "air rights" which today is a common, precious Manhattan commodity.
The sloped roof was designed for solar panels, but they were never installed.
Today, the recessed plaza serves as an entryway for the building, which houses offices in the tower, an attached shopping mall at street level, and funnels thousands of people into a busy subway interchange at the intersections of the 4,5,6,E, and F trains.
This building is a special place to me ... I used to work right across the street from this building, and at the same time one of my best friends worked there. I used to wait outside to meet for lunch or whatnot all the time, looking up at the building and admiring the complextiy of the integration of the Church, the mall, the subway interchange, the plaza, and the highrise. This model was made as a gift for this friend.
This photo shows all the details included in the model, including a bit of a subway station beneath. Engineered subterrania is a strange obsession of mine. :)
Here are some photos of the real building.