Love Letters of a Portuguese Nun (1977)

Sixteen-year-old Maria finds herself trapped in the Serra D'Aires convent, a seemingly tranquil place that hides a sinister secret. Unbeknownst to her, the convent is operated by a group of Satanists who engage in dark rituals. As Maria struggles with her confinement, she forms a bond with another inmate, discovering the complexities of faith, rebellion, and the fight for freedom. Her journey reveals the chilling underbelly of the convent, leading to a harrowing confrontation with the forces that seek to control her destiny.