The Phantom Baron (1977)

Elfy, Countess of Saint-Hélié's daughter, was brought up with her foster sister Anne, in an old dilapidated castle whose landlord, Baron Julius Carol, disappeared mysteriously some day. The two girls had a playmate, Hervé, the son of the gamekeeper. Now that they are adult, Anne is in love with Hervé while Elfy thinks she loves the young man. One day, the baron's mummified body is found in an oubliette and the secret of the estate is revealed...