I remember watching a movie, late at night, sometime in the mid 1990’s (1996-1999) about a man who falls for a woman who is in actual fact a witch. I don’t remember much of the movie, but I do remember a scene where the guy and the female lead (she is in a white robe) are on a patch of grass at the bottom of a tower (like a gothic style church) and they are having sex on the floor.
The Ninth Gate (1999) Here is the scene: