At the beginning of the twentieth century, due to the spread of helmet diving beyond engineering communities, people started to attend to the remarkable qualities of underwater optics, differing radically from seeing through air. With the revelation of this unfamiliar planetary environment to a broader public, creators across the arts took inspiration from underwater optics to structure fantasy spaces of dream, hallucination, and marvel. To show the properties of underwater optics inspiring these fantasy spaces, this article analyzes undersea paintings by Walter “Zarh” Pritchard, reputedly the first artist to have painted en pleine mer. It then turns to aquatically-inspired works of surrealism, the movement offering the most famous appropriation of underwater optics for the arts, focusing notably on André Breton's L'Amour fou and Jean Vigo's L'Atalante.