Tourism forms an important part of Austria's economy, accounting for almost 9% of the Austrian gross domestic product. As of 2007, the total number of tourist overnight stays is roughly the same for summer and winter season, with peaks in February and July/August. In 2007, Austria ranked 9th worldwide in international tourism receipts, with 18.9 billion US$. In international tourist arrivals, Austria ranked 12th with 20.8 million tourists. Vienna attracts a major part of tourists, both in summer and winter. Salzburg receives about a fifth of tourist overnight stays compared to Vienna, which ranks it 2nd in the summer season. In the winter season, a number of winter sport resorts in western Austria overtake Salzburg in the number of tourist overnight stays: Sölden, Saalbach-Hinterglemm, Ischgl, Sankt Anton am Arlberg, and Obertauern. Visits to Austria mostly include trips to Vienna with its Cathedral, its "Heurigen" (wine pubs) and romantic Waltz music events. Worth a visit are Salzburg, birthplace of Mozart, Innsbruck, capital of Tyrol surrounded by the Alps, and the Danube valley with its vineyards, for example the Wachau or Dunkelsteinerwald, which are between Melk and Krems. In the western part of the country the province Vorarlberg reaches the Lake Constance, in the eastern part Neusiedler See. The three most visited landmarks in Austria are Schönbrunn Palace (2.590.000 visitors per year), Tiergarten Schönbrunn (2.453.987 visitors) and Mariazell Basilica (1.500.000 visitors). Of great touristic importance are the Austrian skiing, hiking and mountaineering resorts in the Alps as well as family-friendly recreation areas. The same applies to the numerous Austrian lakes. For visitors interested in Media Art, there is the Ars Electronica Center in Linz. Since 1979 this center has organized the Ars Electronica Festival and presented the Prix Ars Electronica, the worldwide highest-ranked prize for media art.