As a child Martin Thim was fascinated with derelict relics of heavy industry and the military. “It was something I first discovered when my parents and I explored a disused submarine in Estonia,” he says. So when the entrepreneur began working on the old coal bridge in Aarhus’s Sydhavnen in 2013 he knew it had potential.

An ex-industrial area of Aarhus, Sydhavnen was being gentrified and developed as artists and small entrepreneurs began moving in. However, Thim felt that unimaginative office blocks and executive homes would not be in keeping with the area. Beneath the bridge stood an old carpark, inhabited mostly by rough sleepers and drug users who would huddle in grotty shelters. Though Thim wanted to improve the area, he didn’t want to drive anyone out. His design now gives the carpark’s inhabitants better shelters and access to toilets. A zero-waste café has been built and a skate park and basketball court will follow.

By working with occupants around the coal bridge rather than driving them away, Thim hopes to avoid the more toxic side effects of gentrification in the area – and to turn the bridge into a mine High Line.

US cities, Jason Roberts decided, take too long to change. When he thought his Dallas neighbourhood could benefit from a reintroduction of the streetcar that last rumbled through half a century earlier, he didn’t ask the city-planning department. Instead the IT consultant created a website for the Oak Cliff Transit Authority and within three years convinced the federal government that the project was worth funding. “I knew the traditional trajectory for a major public-works project was 20 or 30 years,” he says.

The Dallas Streetcar now rolls again through Oak Cliff, a big step towards making the Bishop Arts District – where Roberts has four businesses, including an outdoor-goods shop – less reliant on cars. The 44-year-old also runs the non-profit Better Block Project and the Team Better Block consulting firm to spread the gospel of guerrilla urbanism. “We’re trying to fix entire cities,” he says. “But maybe the best way to change them is one block at a time.”

Build a dance space in the middle of a city, with music powered by an old coin-operated washing machine, and people will come. That’s what the founders of Gap Filler discovered in 2011 as Christchurch recovered from major earthquakes.

Dr Ryan Reynolds and Coralie Winn, who have art backgrounds, and Andrew Just, an architectural designer, invited the community to help bring life back to vacant sites and remedy a post-quake dearth of culture. The intention was to do “a project or two”, Reynolds says – something whacky, creative and fun, blending performance and temporary architecture.” . Gap Filler has since facilitated more than 70 highly visible projects, including a cycle-powered cinema, a venue built from shipping pallets and a giant outdoor arcade game. Early on the founders made their first and strongest policy decision: not to repeat themselves. They haven’t run out of ideas yet.

Back in 2012, Pedro Borges wanted to see a film in Lisbon when he ran into a problem. “There were no cinemas left in the centre,” he says. “If you wanted to see a movie you had to travel to a multiplex out of town.” The realisation inspired the film distributor to act. “Cinemas are places where people can meet and gather. I wanted to create a community space for people living in the heart of Lisbon.”

After corralling the bank for a loan and attaining a grant from the city, Borges rebuilt Cinema Ideal. Founded in 1904, it had been an important local cinema throughout the 20th century but by the mid 2000s had fallen into disrepair and was only used to screen adult films. Borges acquired the building in 2013 and invested €600,000 in updating it.

The cinema reopened in 2014 and today it screens Portuguese language films and international arthouse movies. About 40,000 people visited the cinema in 2017. “I think Lisbon needs six or seven cinemas like this around the city,” says Borges. “We need the town hall to invest in culture and to integrate it into the city.”

Toronto has about 300km of alleyways – or laneways – running through the city. Often these feature nothing but skips and discarded furniture. Michelle Senayah reasoned that if they could be cleaned up they’d present a social, cultural and economic uplift for the city. “Laneways have been treated as if they’re mono-functional,” the urban developer says. “The city’s population is growing and we need more space so it makes sense to reconsider their use.”

In 2014 she founded The Laneway Project to get more out of the alleys. So far it has incorporated design-led lighting installations into previously under-lit alleys; piloted the idea of transforming certain spaces into fully functioning cycle paths; initiated conversations on the development of housing in laneways; and researched the idea of building Toronto’s first laneway public market. Crucially, city hall is taking note. “We aren’t seen as this novel community group any more,” says Senayah. “We’re now actually seen as a viable part in shaping how our city develops.”

When Lebanon’s civil war ended in 1990, Mona El Hallak was a young architect in Beirut. Looking at the devastation left by the bullets and bombs, her ambition was to rebuild the city. But much of Beirut wasn’t being developed in a way that was respectful of the city’s past. Many of the Ottoman mansions were replaced with skyscrapers. Then she discovered the old Barakat Building.

Built in the 1920s and 1930s, it was used as a sniper’s nest by militia during the war. When the building came in the crosshairs for development, Hallak campaigned for about 25 years to save the plot from being levelled and built upon. After securing a €15.4m grant from the Lebanese government and advice from the French government, Hallak was able to turn it into a war museum: Beit Beirut, AKA The House of Beirut. An archive and exhibition space, the building is an exhibit in itself – the architecture offers a glimpse of prewar Beirut, while bullet holes and graffiti tell the story of the war.

Thiago Vinícius grew up in Campo Limpo, on the edge of São Paulo, a community notorious for gang violence; his younger brother was shot dead there during a police raid. Aged 20, Vinícius led a solution to tackle the poverty that he saw as the root cause of all the crime.

He founded a new kind of bank and a localised currency devised to help Campo Limpo’s poorest. União Sampaio lends money at affordable rates in its own currency. One Sampaio is equivalent to one Brazilian real (€0.23) and can be exchanged locally for goods and services. What sets it apart from similar schemes (such as the Brixton Pound in London) is that profits made from interest are reinvested in cultural projects and social entrepreneurship.

União Sampaio is still growing and helping more people get access to credit in Campo Limpo: more than R$1m (€230,000) has been loaned to more than 1,200 people since the currency was founded in 2013. “Violence is big business in Brazil,” says Vinícius “But we’re taking people out of gangs and into the real economy.”

Karura Forest, a woodland area in Nairobi spread across 850 hectares, used to be a no-go zone. “It was viewed as a den of thieves,” says Karanja Njoroge. “A place where criminals left their victims for dead.” Though this belief wasn’t altogether untrue, it also played into the hands of those who wanted to build on the land. After all, if people feared the forest they wouldn’t fight to protect it.

After discovering an illicit deal to develop the land, Njoroge began a movement to save the forest – and suffered a beating by some heavies hired by a vested interest. A public outcry resulted in a reversal and Njoroge founded the Friends of Karura Forest in 2009. “In 2010 we started fencing the forest,” he says. The change was immediate: Karura registered 300 visitors in its first month and today draws more than 28,000 people a month. “It’s transformed people’s lives,” says Njoroge. “They value the serenity.”

When Wu Ting-an finished his master’s in industrial systems manufacture and management at the University of Cambridge, a return home to Taiwan and a top job at a big corporation beckoned. However, he felt a pull towards his father’s glass-recycling plant – where he spotted a problem. “The profits from glass recycling are thinning,” he says. “Innovation was the only way to continue.”

Wu saved Spring Pool Glass from closure when he took over in 2012 by shifting focus from recycling to upcycling used glasses into consumer products. Now the plant accounts for 70 per cent of the island’s glass recycling and Wu’s vision is to upcycle more of it into art, homeware and building material. His creation of a lightweight, heat-resistant building block made from smartphone lcd glass has won many contracts from developers in the Asia Pacific.

Wu hopes to set an example of how to run a thriving green business, which entrepreneurs in China and Hong Kong can emulate. “Now is the era for environmental businesses that meet growing urban needs.”