This article appears in Volume 36: Discovery.

"Rooftops were made to be walked on," says freerunner Simon Nogueira. "They have to be - otherwise, how would people get up here to repair them? That's why they're peppered with ladders and access points."

Paris is the home of parkour. The first group was founded here by David Belle in 1997. Yamakasi, as the original nine named themselves, drew inspiration from Asian martial arts and military combat training to repurpose ordinary objects and buildings as an obstacle course to help develop physical and mental strength. It was more than a sport: it was an art form and a way of life.

Nogueira, who has been freerunning since he was 13, is founder of the French Freerun Family, a group of parkour and freerunning enthusiasts who we have joined, seven storeys above the French capital. Beneath our feet are television aerials, terracotta chimney pots and the sloping zinc rooftops of Paris's lean Haussmann buildings.

Up here, above the city's green parks and gardens, the freerunners have met people reading, drinking, picnicking, sunbathing and even copulating.

In the words of one of the French Freerun Family's youngest members: "everywhere can be a playground if you make use of it."