Love Letters of a Portuguese Nun (1977)

The devil is in the details...and in everything else at the Serra D'Aires, a convent secretly run by people of the Satan-worshiping stripe. That's where Susan Hemingway ends up in Love Letters of a Portuguese Nun (1977), and it won't end well! Poor Susan is tortured and assaulted by men, women, and the devil himself. A letter to God gets her into the unfriendly hands of the Inquisition in this devilish bit of exploitation from Germany.