A young man stands poised on the edge of a roof, two storeys above the hard concrete of a London street.
Maintaining concentration is key when practising Parkour
He rocks back on to one foot and with a sharp intake of breath his body snaps into action, clearing the void below.
His fingertips hook the bottom edge of an adjacent balcony; hand-over-hand he climbs the railing, finding footholds where none appear to exist.
He vaults neatly over the top of the rail and disappears into the shadows. Welcome to the art of Parkour.
Parkour involves finding new ways of crossing an urban landscape - vaulting, leaping and climbing, with a grace and fluidity of movement more akin to dance than sport.
'Freedom to move'
But it is much more than an adrenalin-pumped pastime - described by its leading exponents as a philosophy, or even a way of life.
David Belle, 33, is widely credited with having founded the sport as a teenager in the Parisian suburb of Lisses.
He described the built-up environment as his "playground" and said he found freedom by breaking out of the physical constraints of his surroundings.
"We know what it's like at ground level, we've been walking the same paths for years. But no-one has ever taken this route," he said in a television interview.
He said his passion was driven by "a need to move" and the physical and mental challenge of overcoming any obstacle using the human body alone.
The practice quickly gathered a cult following in France but it was the BBC trailer Rush Hour in 2002 that brought the fascination of Parkour to an international audience.
The film, showing Belle crossing a gridlocked city via the rooftops, was shot without wires and included a breath-taking building-to-building leap, 60m (200ft) above the street.
Two documentaries followed - Jump London (2003) and Jump Britain (2005) - featuring Sebastien Foucan, who had practised with Belle growing up in Paris.
Although the pair have gained global stardom - appearing in lucrative advertising campaigns and films - they stress the inner spirit of Parkour is not about financial gain or prestige.
"I always thought of Parkour as an art," said Foucan, who is to make his acting debut in Casino Royale as a terrorist hunted down by Daniel Craig's James Bond character.
"When I practise my art I feel a real connection between my body, spirit and my environment," he told the BBC News website.
The Bond chase sequence is being billed as one of the most ambitious in the history of the action series but Foucan is quick to point out the dangers of reckless copycat stunts.
"I never push my limits. I'm now lucky to practise my high-level moves with professional safety people around me.
"Parkour is not about looking for danger and impressing people. It's not about jumping gaps; it's about movement and flow - never forget the fundamental basic moves," he said.
Drilling the basic techniques - Cat Leaps, Tic Tacs, vaults - is the only way to master the art and avoid picking up injuries, according to several websites dedicated to the practice.
Urban Freeflow (Uf), one of the leading Parkour networks with about 14,000 members worldwide, has set up workshops to give beginners the chance to learn the basics in a soft environment.
Parkour is a visually stunning art-form but Uf's founder, Ez, said casual viewers often fail to realise how much hard work the athletes put in to achieve that level of performance.
"In the past a lot of people made the mistake of jumping in at the deep end and found out the hard way there are no shortcuts to becoming proficient at Parkour.
"The workshops help beginners ease their way into the discipline through low-level drills with the emphasis on safety and sensible practice," he told the BBC.
London-based Ez said the enthusiasts turning up to Uf's sessions are "a mixed bag", aged from eight to 55.
No-one is excluded from practising Parkour; all you need is a pair of trainers and a little imagination.