I'm building sand castles in the sand.

现在我正在沙堆里建城堡呢。

youdao

And now I'm building sand castles in the sand.

现在我正在沙堆里建城堡呢。

youdao

So when we say someone is "building castles in the sand," we mean they are creating something that won't endure very long.

所以我们说一个人是在沙子上建造城堡，就是说他创造的一些东西不能坚持很久。

youdao

The tide can be treacherous but the golden sand is ideal for picnics, building sand castles, watching kite surfers and, when the tide goes out, paddling in the lagoons.

BBC: Mini guide to coastal Norfolk