We had this movie when I was a little kid, in the late 80's. I think it had a dragon and a sword and the cover, and was filmed in black and white.

It begins with a witch brewing something which makes a lot of strange noises, then switches to a garden (and a woman?), and then to some knights in a castle. The knights go on a trip and fight a large monkey creature which throws logs at them. They meet witches or vampires who has transformed themselves into beautiful women to seduce them. They wander through a swamp, where the main character is saved by his magical sword pulling him up. They come to some caves where they see some men with strange skin who are suffering and calling for help, and one of them end up being trapped with them (I think).

At the end they arrive at a castle, where a woman is running around, trying to escape. She is scared by some strange, horrible statues, runs up some stairs and is captured. She is tied up in front of a dragon to be sacrificed, and then the hero comes and kills it with the magical sword.

What is this movie called?

Sounds like,.

The Magic Sword (http://www.imdb.com/title/tt0056211/) (62)

That's the one. So it was in color after all. Thank you very much : ). I did not find it when I searched imdb by myself.
I see that imdb has a link to a site that streams the whole movie, and it's funny how I recognize so many details, even the tone of voice they are speaking in : ).