The story
In 1919, when Alsace-Lorraine returned to France, the French Government offered the building to the city of Strasbourg, which in turn offered it to the Strasbourg music conservatory, at the behest of its new director Guy Ropartz, who was refusing to occupy the Palais du Rhin opposite.
On 25 September 1944, the east wing of the building that contained the Chamber of the Assembly was destroyed by American bombing. It was reconstructed between 1950 and 1957, this time with a theatre auditorium replacing the assembly chamber. Michel Saint-Denis, the director of the National Theatre of Strasbourg at the time, entrusted this work to the architect Pierre Sonrel, who had recently worked with him in London restoring The Old Vic, which itself had been badly damaged by wartime bombing.
In 1995, the façade, roofing, and the entrance on Place de la République were classified as a monument historique.
Conservatory
In 1922, the Conservatory of Strasbourg (founded in 1855, the same year as the Orchestre philharmonique) was moved into the upper part of the building and several teaching rooms were built in as well as a concert hall. In 1995, the building wasn't deemed suitable enough for teaching music any more and the conservatory had to move out; it was subsequently relocated in the Cité de la musique et de la danse, a state-of-the-art building inaugurated in 2006. The concert hall has remained unused since. In 2016, the monumental pipe organ, a 1963 work by organ builder Curt Schwenkedel, was restored and moved into Saint Stephen’s Church, where it started a new life as a church organ instead of a concert organ.
From Wikipedia’s article on National Theatre of Strasbourg, shared under CC BY-SA 4.0.3