Dan sets out to reveal how architecture enables people to live together across the world. He finds vibrant communities in extraordinary buildings and towns across the globe - but why do some places succeed and others fail?
He visits Brasilia, an ideal city built by communists, which is now the preserve of the super-rich. In the Middle East he travels to Damascus, the oldest continuously inhabited city in the world, to unravel the secrets of its longevity.
The Rockefeller Centre in New York is one of the city's most famous skyscrapers - but how did a building borne from the American Depression become a 'city within a city'? And Dan explores Dharavi in Mumbai, the biggest slum in India - a functioning home to millions, but now under threat of demolition.