The quality of being relaxed and fanciful is dreaminess. The dreaminess of a breezy summer afternoon spent lounging in a hammock under a willow tree is hard to beat.
Dreaminess is a state that can be described in a few different ways. There's the dreaminess of a daydream, when you're not quite asleep but nearly dreaming and totally at ease. There's also the dreaminess of someone who is impractical and distracted, and the dreaminess of something that feels slightly unreal, in a nice way, like a good dream: "The movie's dreaminess is perfectly reflected by its slow, hypnotic soundtrack and soft, muted palette."