A small castle built out of wet sand on a beach, usually by children, usually with a bucket and a plastic spade. You pack damp sand into the bucket, turn it over, lift it off, and a tower stands there; do that a few times and add a wall and a moat around it and you have a sandcastle. It does not have to look much like a real castle — any little heap of shaped sand with towers counts. Written both as one word and as two ('sand castle'), and the two-word spelling is more common in the US. What matters most about the word is the feeling attached to it. Everyone knows the tide comes in and the castle goes. So English uses it for anything built with care that will not last: a plan, a business, an argument that 'was a sandcastle', or something that 'washed away like a sandcastle'. When you hear it about a grown-up thing, that is nearly always the point being made.

沙堡（在海邊用沙堆的城堡）；比喻經不起考驗、很快就沒了的東西