Stand by Me
I had watched this movie with my brother as a child so it made me nostalgic rewatching it.
The best thing about this movie is the fact that it's slow: nothing too exciting happens, there's no suspense at all, and plus it's not too long. It's slow, but in a very positive way...it is not stressful, it's peaceful.
And I also love the main song which is incredibily relaxing.