"And so castles made of sand / fall in the sea / eventually." -- JimiHendrix?
I love sandcastles; that's the whole reason to live near the coast. A relaxing experience that just isn't easy to describe. -- EricSpehr
Sand castles are properly built just ahead of the incoming tide. Very impermanent, very WabiSabi. Much like the text we leave here on the wiki (after all, we even have a page called WikiWikiSandbox).
Ah, the humble sand box. A place where children play and cats do their business.
Or professionals can make very elaborate structures. And Monks or Aboriginals, elaborate SandPaintings?. Well their "box" may be more open-ended. But worlds can be seen in grains of sand, by adults as well as children though the latter tend to have more of a BeginnersMind.