Live Together in Peace; U.N. Flag; Donaupark, Vienna; Birds in Flight; and Flags. The two Donaupark stamps feature the United Nations buildings in Vienna. A United Nations center consisting of several buildings was opened there in 1979. The center serves as a U.N. conference site and provides office space for some U.N. agencies. These stamps were the first ones to be issued for use only at United Nations headquarters in Vienna. They are all adaptations of previous U.N. issues.