castles in the air
空中楼阁
书面/口语·形容空想或白日梦
英文释义
to have unrealistic or impractical dreams or plans
例句
He's always building castles in the air, dreaming of becoming a millionaire without working.
典故来源
源自中世纪欧洲，比喻不切实际的幻想，如同在空中建造城堡一样虚幻。