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.

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

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