Filming took place at the royal palace built by King Felipe II, El Escorial Monastery, 45 kilometres north west of Madrid and at the Alcázar castle of Segovia. The Alcázar purports to be the Palace of the Duke of Pastrana in Guadalajara, which, although still standing elsewhere, was not used; probably the real thing was considered too unrealistic. The Escorial on the other hand was accurately used for the scenes depicting Felipe II.
We see the main entrance to the Alcázar at the beginning of the film when the King arrives to be greeted by the Princess of Ebolí and her son, and again when the Cardinal arrives.
When Antonio risks all to go and see the Princess, we get an even better if brief view of the castle in all its splendour.
There is also a view from above as the Princess returns from her incarceration and a fine view of the battlements and wall as Antonio scales it to be with his beloved.
Unfortunately Antonio seems to have overcome torture better than the Princess dealt with servant deprivation.
Paul Scofield made his film debut as Felipe II and won a BAFTA award as most promising young actor in this film, despite his barely credible beard.
Olivia de Havilland stars in the title role (wearing a black eye-patch as Ana de Mendoza, Princess of Eboli) and Christopher Lee appears in one of his earliest films.