Griff Rhys Jones puts the glossy brochures aside to try and get to the heart of New York, London and Paris and how they shape the people who live there.

He starts off in New York. Over the past 100 years, a child has been born, on average, every four and a half minutes in New York. What sort of place have they arrived in?

Griff spends 24 hours meeting New Yorkers, from the man whose job it is to hoist more than 70 American flags every morning, to the birth of a baby late at night.

In Brooklyn, a Greek family runs a thriving business, serving the best New York breakfasts, and Griff tries his hand at waiting on the hungry clientele, getting to grips with the "extremes of carbohydrate, fat and sugar that an American in New York can eat for breakfast".

As the morning rush hour reaches its fevered pitch, he visits Grand Central Station, described by Griff as more like a temple than a terminal. Some 700,000 people pass through the main concourse every day, the equivalent of the entire population of San Francisco.

New York is famous for its skyscrapers and Griff explains that in the early part of the 20th century, tycoons battled to build the highest buildings. The Woolworth Tower was a prime example, built in 1913 and paid for in cash by Frank Woolworth. He wanted it to be the tallest building in the world, taller than the Metropolitan Life Insurance building because they once refused him a mortgage.

In a city of towering buildings, window cleaners are a special breed, and Griff joins veteran cleaners Brent and Vincent at the top of a 30-storey building, and climbs over the edge. His confidence is not boosted when Brent and Vincent can't seem to agree how the equipment works. This was, Griff says, "the single most terrifying experience of my life".

New York is a city of contrasts, and after visiting the Carlyle Hotel where a suite costs over $7,000 a night, Griff travels across town to the Lincoln Correctional Facility where long-term prisoners are taught how to adapt to normal life again.

In Queens, he visits a factory founded more than 150 years ago that employs 450 people to make exactly the same thing that they first manufactured in 1853, Steinway pianos. Each piano has to pass the ear of one man. But although Wally has worked at Steinway for 45 years, and carries out the final tuning, he only learnt to play the piano four years ago.

James Allen has invented an inspired way of raising funds for a rehab centre in the city. He brought together a group of addicts to form a choir in Harlem. A visibly moved Griff describes sitting in the midst of a "waterfall of voices" as "a profound experience for me".

As day turns to night, Griff goes backstage at a Broadway production, and then falls into step with a herd of Indian elephants from the Barnum Circus.

He is invited to attend a traditional Russian Jewish wedding and meets the family and friends who have made New York their home. As the celebration gets wilder and the vodka flows, Griff leaves for his final appointment.

It's 3am and Griff is waiting at the children's hospital to meet someone who is taking his time arriving.

Born to Peruvian parents, Ivan is the first in their family to be a native New Yorker.

As the new day starts to break over the city, Griff wonders what New York will be like as Ivan grows up, and expects that, like millions of others, he will find that change and continuous invention are part of the excitement of this remarkable city.