On the wall of Bianca Castafiore's dressing room can be seen a poster for Teatro La Latina (a well-known theatre in Madrid, property of Lina Morgan), announcing performances by, between others, Antonio Casal, Juanito Navarro, Marujita Díaz and Lina Morgan herself, all of them well-known Spanish comedy or musical performers.
The castle of Marlinspike (Moulinsard in French) is based on an existing French castle: Cheverny, on the Loire river. Unfortunately, the real castle has two extra towers on each side, recently added. For the movie, they chose the castle of Ecquevilly, which was was at this time a sanatorium - now the city hall. Interestingly enough, two other movies took place in this small city : "Les risques du metier" from André Cayatte (the school is in fact the former city hall), and The Longest Day (1962) from Ken Annakin.