Charlie travels to America to meet Leo Villareal, the artist behind the bridge art project. Back in London, he meets British artist Ben Wilson who aims to transform the Millennium Bridge.

As work on the bridges starts, an Egyptian goose lays an egg putting the tight schedule in a spin; Charlie Luxton abseils down the side of London Bridge and explores the history of Southwark.

After three years of intense planning and coordination, the big day arrives as 69,000 lights illuminate four of London's most iconic bridges in the world's longest piece of public art.