Stockholm, a city made up of 14 islands connected by some 50 bridges, is highlighted in the third-season opener, which examines how Europe's first green capital tackles environmental problems and is an ideal destination for walkers and cyclists

New York is constantly changing; Harlem and 125th Street have been redefined; Brooklyn, the working class suburb, has become a destination in its own right; High Line Park, now stretching above 16 city blocks of the West Village, continues to grow.

The Free and Hanseatic City of Hamburg truly is a metropolis, but with an abundance of green areas and countless canals Hamburg also ranks as one of Germany’s greenest and most attractive cities. Water dominates the landscape in Hamburg. Consequently the city boasts an incredible number of bridges – more than Venice and Amsterdam together!

A look at the transformation of Doha, the capital of Qatar, from a quiet fishing village to a bustling city.