The legendary Loreley has been living for centuries in a grotto beneath the river Rhein in Germany. Every night when the moon is full, she turns into a reptile-like creature craving for human blood. When one girl after another of a nearby boarding school is killed by her, a hunter named Sirgurd is engaged to kill the monster.
http://www.imdb.com/title/tt0071535/Director: Amando de Ossorio
Writer: Amando de Ossorio
Stars: Tony Kendall, Helga Liné, Silvia Tortosa