Salzburg is the fourth-largest city in Austria and the capital of the federal state of Salzburg. Salzburg's "Old Town" (Altstadt) with its world famous baroque architecture is one of the best-preserved city centres north of the Alps, and was listed as a UNESCO World Heritage Site. The city is noted for its Alpine setting. It is the birthplace of Wolfgang Amadeus Mozart and the setting for parts of the musical and film The Sound of Music, which features famous landmarks in Austria, but focuses mainly on Salzburg. Salzburg is a student city, with three universities. Salzburg is on the banks of the Salzach river, at the northern boundary of the Alps. The mountains to Salzburg's south contrast with the rolling plains to the north. The Altstadt, or "old town", is dominated by its baroque towers and churches and the massive Festung Hohensalzburg.