This 1971 Euro Gothic horror film is a fascinating and genuinely chilling find. The story centers on seven tourists trapped overnight within an eerie German castle, where a succubus targets those indulging in the seven deadly sins—lust, gluttony, greed, sloth, wrath, envy, and pride. "The Devil’s Nightmare," a Belgian/Italian co-production, boasts a strong cast and narrative, all filmed on location at a real castl…