空中楼阁的英文：
[Literal Meaning]
air/in/mansion
a mansion in the air

[解释]
虚幻的事物或脱离实际的空想。

[Explanation]
realm of fancy; illusion

[例子]
他会带你出国定居的许诺都是空中楼阁，不会兑现的。

[Example]
His promises to take you abroad to live were castle in the air and will never be fulfilled.

[英文等价词]
castle in the air

A castle in the air/in Spain
空中楼阁

ivory towers
空中楼阁

His proposal was nothing but a house of cards.
他的提议只是空中楼阁。

His castle in the air crumbled.
他的空中楼阁成了泡影。

What he is talking about is just a castle in the air.
"他所谈论的一切,只不过是空中楼阁。"

Their ideas about reforming the prison system are just pie in the sky.
他们打算改革监狱制度的想法纯粹是空中楼阁.

The castle-building habit, the day-dreaming habit-how it grows!
那个盖空中楼阁的习惯，做白日梦的习惯-发展的多快啊！

He returned to his lodging with his head full of castle in the air.
他脑袋里装载着空中楼阁回到了寄宿处。

As a girl she built the usual castles in the air; but all her girlish hopes and aspirations have long been dead.
在她年轻的时候，她也曾建筑过空中楼阁，但她少女的希望和抱负早就全部破灭了。