The fourth-largest city in Austria, Salzburg is known for its great beauty, and for being the setting for the musical and film The Sound of Music. It is the birthplace of Wolfgang Amadeus Mozart, whose childhood home can still be seen there. The baroque Old Town area, dominated by the Hohensalzburg Fortress on the hill, became a UNESCO World Heritage Site in 1996. It is possible to visit the von Trapp family home and other Sound of Music locations. Another famous person born in Salzburg was Christian Doppler, the acoustic theoretician best known for his discovery of the Doppler effect.