Vienna is the capital of the Republic of Austria and one of the nine states of Austria. Vienna is Austria's primary city, with a population of about 1.7 million, and is by far the largest city in Austria, as well as its cultural, economic, and political centre. It is the 10th largest city by population in the European Union. Vienna is host to many major international organizations such as the United Nations and OPEC.
Vienna lies in the east of Austria and is close to Slovakia, the Czech Republic and Hungary. These regions work together in a European Centrope border region. With the close by Bratislava, Vienna forms a 3 million inhabitants metropolitan region, referred to as Twin City. In 2001, the city centre was designated a UNESCO World Heritage Site and in 2005 an Economist Intelligence Unit study of 127 world cities ranked it tied with Vancouver for first for the quality of life.
A variety of architectural styles can be found in Vienna, such as the Romanesque Ruprechtskirche and the Baroque Karlskirche. Styles range from classicist buildings to modern architecture. Art Nouveau left many architectural traces in Vienna. The Secession, Karlsplatz Stadtbahn Station, and the Kirche am Steinhof by Otto Wagner rank among the best known examples of Art Nouveau in the world.