As he walked along, his brain was busy planning hundreds of wonderful things, building hundreds of castles in the air.

当他走着的时候，他的脑子里正忙着计划许多奇妙的事情，建起一座座空中楼阁。

My father built castles in the air about owning a boat.

我爸爸做了拥有一条船这样的白日梦。

Just like castles in the air, this idea is totally impractical.

想法简直就是空中楼阁，不可能实现的！

Your mind was on something not so practical-castles in the air.

你脑子里想的都是些不切合实际的事情——都是空中楼阁。

Their calculations have all been proved to be castles in the air.

他们的算计证明不过全都是空中楼阁。