Felsenreitschule

You guessed it right.
This is the place where Captain von Trapp sings "Edelweiss" and from which the von Trapp family disappear, in the film, The Sound of Music.

From 1926, the Felsenreitschule was used as an open-air theatre for performances of the Salzburg Festival. With the auditorium reversed, the former audience arcades now served as a natural stage setting.

In 1948 Herbert von Karajan first used the Felsenreitschule as an opera stage, for performances of Christoph Willibald Gluck's Orfeo ed Euridice. This was followed in 1949 by the premiere of Carl Orff's setting of the ancient tragedy Antigone by Sophocles, translated into German by Friedrich Hölderlin, conducted by Ferenc Fricsay. Between 1968 and 1970, the Felsenreitschule was again remodelled according to plans by Clemens Holzmeister and inaugurated with Ludwig van Beethoven's Fidelio under the baton of Karl Böhm.

The first Baroque theatre was erected in 1693–94 at the behest of the Salzburg prince-archbishop Johann Ernst von Thun, according to plans probably designed by Johann Bernhard Fischer von Erlach. It was Max Reinhardt who suggested that the Winter Riding School should be converted, and it was also his idea to transform the Summer Riding School (Felsenreitschule) into a theatre. During the first half of the 17th century conglomerate rock was quarried here for the building of the cathedral. In 1693, during the reign of Prince-Archbishop Johann Ernst Thun, according to plans by the Baroque master architect Johann Bernhard Fischer von Erlach, three tiers of 96 arcades were hewn into the walls of the disused quarry so that from here people could watch equestrian displays and animal baiting events.