A rose among the thorns in South American cities, few places have been as successful as Medellin in tackling social problems head-on with urbanism, architecture and greening of the urban landscape. Colombia's second-largest city has gone from drug-cartel hovel to urbanist dream. The work is nowhere near done but Medellin can inspire every other city in the world with its visionary political and social choice and its strong network of urban activists.

Mikael Colville-Andersen lands in Toronto to meet the urban heroes working to make Canada's largest city more livable. A prominent cultural and artistic hub and a haven for foodies, Toronto is the big city that doesn't feel impersonal. With 239 neighbourhoods and people coming from all over the world, it's a multi-faceted and profoundly diverse metropolis.

Often perceived as cold and expensive, Paris is a mythical city, one of luxury, gastronomy and haute couture. But beyond the clichés of the Eiffel Tower, there is another Paris - one of solidarity, wittiness, and repurposing public space. This Paris revolves around change, inspiring solutions big and small to improve everyday life for its citizens. It hopes to minimize traffic, give a new life to the banks of the Seine River, and provide adequate lodging and a sense of belonging.

A chaotic mix of skyscrapers, street markets and hidden alleyways, Bangkok is a vibrant hub of life, buzzing day and night. Dubbed the Capital of Gridlock, Bangkok boasts traffic that is among the worst in the world. The city's future seems paralyzed by recurring political upheavals, but social instability hasn't undermined the locals' fierce will to better their city. They're fighting back, not with violence but with creativity and ingenuity.

Few modern cities evoke as much division as Tel Aviv, with its reputation as a laid-back and permissive party town in a hotbed of conflict and turmoil. The problems of a rising cost of living, deficient public transport, and development conflicts are often put aside in the face of cyclical religious and cultural struggles that have marked its complex history. But people from both sides of the political and cultural divide are working together to create a more functional and united city.

Modern Tokyo is a fascinating urban mystery. The largest urban agglomeration in the world, it is home to 38 million people - more than the entire population of Canada in one city. On the surface, Tokyo feels like an oversized, human-built environment, full of endless rows of towers, glittering neon and fast-moving citizens. But if you dig deeper, this megacity is much more than its impressive size.