The graffiti-strewn walls of a disused brewery are a far cry from the manicured greens of the Open Championship but this is where Berlin's "crossgolfers" play their own underground version of the game.

The sport of "cross golf", otherwise known as urban golf, "street golf" or even "anarcho golf", where players whack balls at improvised targets, has found a natural home among Berlin's wide open urban spaces and abandoned buildings.

And in the old burnt-out Baerenquell brewery in the old East Berlin district of Treptow, a group of six urban golfers, dressed in t-shirts, jeans and hooded caps, are teeing off, oblivious to the sign "no entry for unauthorised people."

"On a real golf course, it's always about etiquette, rules. It's snobbish and elitist," said Eve, the only woman in the group.

"Here, it's less uptight. Anyone can play anywhere. It's for anyone who has the time and desire to play," said the 28-year-old who has been playing the game since 2010.

Next to her, Sven, 37, carefully places his ball on a small patch of synthetic grass he has laid down on the concrete floor.

Cigarette drooping from his mouth, jaunty flat cap slightly skew-whiff on his head, he swings hard at the ball, aiming for a far roof, but succeeds only in sending the astroturf patch high into the air.

The idea of urban golf can be summed up simply: why go to a golf course when you can play in the streets, in the city or in a park?

The exact origins of this "sport" are lost in the mists of time, but specialist websites are agreed on one thing: it was invented in Germany in the 1990s.

Since then, it has become yet another successful German export, with players across Europe, in the United States and as far afield as New Zealand.

Tournaments (often with tongue-in-cheek names such as the "Bratwurst Open") are widespread in southern Germany.

And while Berlin has not yet hosted its own tournament, players here are convinced it is the best place to play.

"I play two or three times a week," says Stephan, a 26-year-old nurse. "This is one of the best places you can find to practise. It's really turns me on."

This group plays a "safety first" version of the game, said Stephan. "We play with synthetic balls. That way, there's less risk of hurting someone or smashing something."

"There are people who play with real balls, but they aren't part of our group. There are black sheep in all sports," he adds.

Apart from that, there are really no rules in urban golf. Each group defines the targets to aim for, the number of shots allowed, its own regulations.

This group has played near the Reichstag building in central Berlin, in the Tiergarten, a huge expanse of greenery in the middle of the city, in stations, an abandoned textiles factory and also a disused swimming pool.

They are considering alternatives: a giant former Soviet military hospital, or Teufelsberg (Devil's mountain) with its derelict American spy station.

This "round" has already taken them more than two hours. There's no real set length of time for a match, explains Stephan, swigging from a can of beer. "You can play until late into the night or just until you're bored."

But for now, all eyes are on Sven, as he prepares to play the tricky next "hole".

"Where's the Trabant?" he shouts, as he stands on the brewery roof searching for the shell of an old East German car he has to hit to win the hole.