Animated Greek mythology movie?

Trying to determine the title of an animated film or short I remember seeing back in the 80's. The main character was a boy. Scenes I recall are where he comes across a lake type place and irritates some goddess by interrupting her in the waterfall. The other is when he's in a real fantasy type space with stairs and a similarly aged blonde girl in a white dress. As he ascends the stairs awestruck by her beauty, she transforms into medusa and he fights her. All I've got I'm afraid. Older cartoon, hope I didn't imagine it all 20-some years ago.