To whet your appetite and keep your writing fingers limber, take a good look at the photo, or let a prompt settle in your mind. Set a timer for a reasonable amount of time, be that five, fifteen, or thirty minutes. Then start writing.
This stack of stones is the magical center of the universe. Write the story of how your character discovers the spot and uncovers its secrets.
Do you like to clamber over rocks at the coast, skip pebbles across a pond, or climb boulders? Did you collect rocks when you were a child? Why or why not?
Write about coastal erosion and how people can be responsible beach visitors.