"I could see downtown to where the UN balanced itself in the dark, like a weird, green, Martian honeycomb."

This is a reference to the United Nations Headquarters in New York City. It is a group of four buildings, the largest of which, the Secretariat, was built between 1949 and 1950. The complex as a whole was completed in 1952.

The narrator's description of the building is very imaginative and very apt! 

United Nations Secretariat Building, New York
Creative Commons AttributionUnited Nations Secretariat Building, New York - Credit: Matthias Ott, Wikimedia Commons