The Zhizhai window, or hung and removable window, at the Forbidden City in Beijing. [File photo]

Many features of the architecture of the Forbidden City help to relive the summer heat. The Zhizhai window, or hung and removable window, is one of the great inventions. The upper part can be hung up for ventilation, while the lower part can be removed to allow more light in.

Besides, the royal family of the Qing Dynasty can even enjoy an air-conditioned room in ancient times. As the icebox often has air holes, it can cool the temperature of the room.