I saw this movie on TV. It was about this young man who was on some kind of quest.
I do not remember much about it but I do remember he was on a quest and he asked this island for help which turns out to be a whale or some kind of fish that hardly ever moved so animals and people lived on it. It had trees and grass growing on it

It agreed to help the young man on his quest
Sorry I do not remember much. It was shown on TV late 70's early 80's