Introduction to United Nations City: Vienna United Nations City (Vienna International Center) is the third largest seat of the United Nations after New York in the United States and Geneva, Switzerland. More than 4,000 employees from the International Atomic Energy Agency, the United Nations Commission on International Trade Law, the United Nations Industrial Development Organization, the United Nations Office on Drugs and Crime, the United Nations Office for Outer Space and other agencies work here. United Nations City allows individual tourists to take guided tours without reservation.