I have always loved creating sand sculptures on the beach. Even knowing the wind and ocean will eliminate the hours spent creating the structures. It reminds me how temporary we are in the ebb and flow of natures tide. How the methodical and seemingly infinite movement of water will bring everything back to minute particles of sand perfectly flat and smooth on the shore.
Most of my structures aren't even close to resembling a castle. Usually just a mountain or hole surrounded by a moat or valley. My shovel is typically just a plastic glass and also serves as the mold for the towers (assuming some wet sand that will stick together.
It's always fun to return to the point of construction to see the ruins. Sharp lines become smooth; Big holes become shallow; Tall mountains become mounds; and in time the everything returns to the beginning.