Here everything happens either very high up or very low down. High above, the driving schools open offices on the roof of houses and designer firms build skyscrapers instead of boutiques. Down below, seven and a half million people spend two or three hours a day in the underground, turning it into a parallel city, where unwritten rules dominate, with which everyone complies: no talking loudly on the telephone or with the person next to you.

Everyone is doing something here: sleeping, reading, buying shares, watching a film, writing text messages. But always in silence.