Spiritually, sand represents the impermanence of the physical life and can suggest having to approach death or change in some way. The sands of time is an image much used in poetry and lyricism. Sand in a dream suggests a degree of instability and lack of security. When sand and sea are seen together we are not feeling particularly emotionally secure. When the sands are shifting we are probably unable to decide what we require from life. If we are conscious of the sand in an hourglass we are aware of time running out; we perhaps need to be certain we are making best use of our resources. Sand can represent impermanence. Because they will inevitably be washed away by the tide, building sand castles in dreams suggests that there is some doubt about the validity of a project in which we are involved. They also indicate that the structure we are trying to give to our lives does not necessarily have permanence and may be an illusion. You might also like to consult the entries for Beach, Digging/Excavation, Hourglass and Time.