A sandcastle is built with joy and washed away by the tide. It is read as creativity, impermanence and plans that are lovely precisely because they do not last.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.