But they aren't cat-burglars-in-training, reports CBS News correspondent Sheila MacVicar. They're British managers, teachers and health workers, out for an evening workout - some "Parkour" training, led by Dan Edwards.
"You can jump into it. It's just a case of being comfortable enough with the leg to land," says the veteran of the urban sport that has literally leapt onto the scene over the last decade.
Parkour came from- the word means "route" or "path". It's an edgy discipline that owes as much to martial arts as gymnastics.
Shirley Darlington first tried it nine months ago, but now glides with surprising agility and grace through hard urban landscapes.
"It feels great when you can move fluidly... It's a great feeling when you can just go over, over and under and up. It's quite cool," Darlington says.
It may be cool, but also tough.
It's not about how you look, it's about what your body can do," says Naomi, another eager Parkour student.
Made more popular by TV ads and movies, the first Parkour personalities were chiseled young men moving against city landscapes.
But, in, Parkour is now graduating from the street to the school gymnasium.
"The kids are attracted because it's cool and young and it's used in movies all the time," explains Edwards. "It's in the social consciousness at the moment."
Teachers say Parkour, which has no rules, no teams and no equipment apart from a decent pair of sneakers, seems to hold appeal for kids who aren't usually enticed into sport with a basketball or a baseball bat.
"It really empowers them to be seen as athletes amongst their peers, which is really the biggest thing," says P.E. teacher Matthew Sheppard.
"It's something different from everyday things," says student Ivanilza Damat. "Everything has certain boundaries, Parkour hasn't got any boundaries, it's like jumping over the boundaries, really."
School boards in the U.K. are investing in Parkour training because a pilot project in inner city schools linked training sessions to an impressive 30 percent drop in juvenile crime.
"It makes you very autonomous, very self reliant," says Edwards. "It makes you understand your potential, physically and mentally."
It's all about overcoming your fears and fatigue. Or, as Shirley says: "I can control this barrier, I can control it and push past it and keep going."