Where was The Music Teacher filmed?
1988 film by Gérard Corbiau
The Music Teacher (1988) was filmed in La Hulpe, Chimay Castle, Olloy-sur-Viroin and Solvay Castle, 4 places named in its Wikipedia article, in Belgium. Wikidata records no filming location for it at all, so the article is the only recorded source. Each place says where its claim comes from.
Places per Wikipedia's article
The Wikipedia article names 4 places. Each links to the sentence that says so.

