The Sand Castle is the story of an afternoon of a small boy who is left on the beach with his sister. He wanders about and picks up stray objects — a seashell evokes an unconscious response and, in a reverie, he builds a sand castle. Several people, who are ultimately, directly or indirectly, affected by what he is doing, gather to watch. Presently a storm drives them away, and the boy falls asleep with his sister under a beach umbrella. In a dream he explores the interior of the sand castle, meeting the people who had watched him build it.

The film's creator, Jerome Hill, originally intended to illustrate Jung's psychological theory of sleep, but he rapidly abandoned this specific purpose and the film acquired the stature and evocative power of a work of art. It is a "double" film, built around the contrast between the conscious and the subconscious existing in sleep. To emphasize this contrast, Hill has shot the first sequence in black and white and the dream sequence in colour, in which he introduces a novel form of stop-frame animation: paper figurines against paper sets painted to resemble a nineteenth-century theatre. This versatile director majored in music at Yale and has studied painting in Rome and Paris. He has a number of documentary films to his credit including the Academy Award winner Albert Schweitzer. The Sand Castle is his first feature film.