A city with a history of the trend and counter trend, San Francisco is home to living a greener and simpler life.

With more than 50 percent of its population under the age of 24, change is being ushered in by Cape Town's youth; optimism, hope and resilience pit themselves against the lingering wounds of apartheid.

Tel Aviv is the international capital of Bauhaus architecture and an example of tolerant co-existence.

Bangkok is a city in motion; traffic is impossibly dense: cars, boats, overcrowded streets; beneath the culture of chaos, this Buddhist city possesses a deep and permanent respect for well-being.

Helsinki, a leader in social policy, innovator in telecommunications and the sauna capital of the world, is composed of 150 islands.

More than 80 languages are spoken on the streets of the Australian city of Melbourne.

Having been defined by NASA, petroleum and cowboy ways, Houston is surprisingly liberal.

Hot water geysers dominate Reykjavik's landscape.

Frozen in time, Havana reveals some of its secrets; meet the photographers of the Cuban revolution and learn about the reality and role of socialism, baseball and salsa dancing, and visit the rooftop gardens that feed 90 percent of the local population.

Moscow is located between five rivers and seven seas and is known as the global capital of the outrageous.

The oldest city in France is a city of contradictions.

The people of Buenos Aires, known as the Paris of the Americas, live life to the fullest.

Lisbon has been transformed over the past 20 years into Europe's most cosmopolitan city.

Known for its gondolas, its sunsets and amazing light, Venice is the world's only medieval city still standing today. For 1000 years, Venice was a trading capital, an economic power linked to the sea. It was the centre of activity and the warehouse for tradesmen, seamen and artisans. But annual floods and 21-million tourists a year are compromising the city on stilts, and Venitians struggle to find a solution.

For several years, Singapore has been neck and neck with Shanghai as the largest port in the world. Made of 64 islands on a territory about the size of Toronto, Singapore is also a country. Fifty years ago, the archipelago of tropical forests was covered in tiny wooden houses - it is now one of the world's most eccentric and vibrant cities, host to some of today's most ambitious architectural projects.

In a city that keeps growing, the question for Istanbul is "where to put all the people?" Due to the high density and historical importance of its buildings, creating or renovating structures is an issue. But the city continues to welcome an eclectic group of cultures - booming economically and socially - and becoming one of the most dynamic cities in the world.

Land of oranges, Valencia is a critical city of importance for Spain. Its strategic location on the Mediterranean attracted Greeks, Romans and Moors - who have all taken turns at its control. During the Roman Empire, Valencia was a supply restocking city for ships, and a major trading hub. Today, with its parks and long beaches, Valencia has no car congestion, just the sea and the perfect climate.

Nestled between the sea and mountains, Vancouver is both a city of water as well as an outdoor haven, which explains its citizens’ obsession with sports. Just 125 years ago, this city was virgin forest and Heidi finds out how such a young city managed to develop in population, size and importance in such a short time.

It is said that Copenhagen is primarily designed for its people: it’s very practical and very down to earth. In the Danish capital, everything works extremely well. In terms of energy, the city has done its homework and now ranks among the world leaders in generating clean energy and sustainable development. In the port of Copenhagen, 27 windmills adorn the landscape. But the port here isn’t an industrial mess – between the ships, the water is clean, and the docks are used by locals for casual family swimming.

Valletta, the capital of Malta, is undoubtedly the smallest city to be explored by the series…but it’s definitely worth the trip. Officially recognised by UNESCO as a World Heritage Site in 1980, Valletta was founded in 1565 and provided a safe haven for just about anyone.

The symbol of new Russia, St. Petersburg is a link between a large inaccessible country and the world.

Boston has a high concentration of higher education and research institutes.

Salvador de Bahia's culture including street parties and capoeira.

After rebuilding itself, Panama City is becoming a popular retirement destination.

Discover the beauty and complexity of Hong Kong through the lens of renowned photographer Heidi Hollinger as she explores the essence of this vibrant city to capture its spirit and soul.