Long time searching without results ?

I remember only this:

-A lady redhead short or long hair

-In a dark blue dress or tunic

-Sleeping outside next some kind of castle ruins

-A guy in a tunic meditating, put somekind of gem in her mouth to be invisible

-Then the guy sneak near this lady and grab her asscheeks ?

Color movie of the 80s, not sure, but its old. That scene is stuck in my mind for long time, hope you help me see it again, would be great!