The Sinful Nuns of Saint Valentine (1974)

Lucita has been locked away in a convent by her family in order to keep her away from her lover, Esteban. The pair make plans to elope, but Esteban is accused of heresy before Lucita can escape. Hiding in the convent, Esteban discovers the horrifying depravity of the convent's abbess, Sister Incarnation. Can Esteban rescue his love from this madhouse before the inquisitor discovers what is going on and has everyone executed?