Red-Haired Devil-Woman Attacks Students in Mansion

by Carlos
(Ecuador, South America)

I saw a 60's or 70's film years ago about some students that go to an old castle or mansion.

Either they go there with a red-harid woman, or they pick her up along the way on their bus. At night, the woman transforms into a devil with red eyes and long fingernails.

One by one she kills the students, and their bus is thrown into the abyss. This woman's face is both annoying and terrifying.

Please help me find the name of this movie. Thanks a lot!