The phrase "to build a sandcastle" means to construct a small structure made out of sand, typically on a beach or in a sandbox, by shaping it with your hands or using tools like buckets and shovels. Full definition
Kids will love building sandcastles on the golden sands and hunting for fossils by the Red Crag cliffs. (tripsavvy.com)
While we still weigh the pros and cons of nomadic travel (you can read about my fears here) not a day goes by that I don't wish to be sitting on the beach building sandcastles with my boys. (carpediemourway.com)
So, succumb to that inner child who builds sandcastles at the beach and watches them as they wash away with the tide. (ericfirestonegallery.com)