The centre's unmarked entrance seems fitting - the project inside is one of the Jewish community's hidden treasures.
Despite being based in the centre of Hendon, north-west London, the Boys Clubhouse is largely unknown within Anglo-Jewry. Yet its essential work gives hundreds of young Jewish men a new start in life.
Run by Ari Leaman, the Clubhouse is central to efforts to tackle addiction problems and criminal behaviour among Jews aged 14 to 25.
Filled with sofas, pool tables and Playstations, it looks like any other youth club. The main difference here is that the patrons are often convicted criminals recovering from addictions or overcoming homelessness.
A reformed burglar and ex-drug addict were among the young men hanging out during my visit.
The club helps around 60 boys a week, acting as a drop-in centre, providing counselling and even the first steps towards a career.
Many come to regard it as a home, and Mr Leaman and his colleagues as family.
He said: "We are the last port of call. Most of the kids we come across have had a difficulty in their childhood which has impacted on their adult life.
"I've come across cases where a kid has taken a knife to his mother and been thrown out of the house. It's a small number but it happens.
"We get referrals from Norwood, Jewish Care, community rabbis, the police. We're apolitical, we are not affiliated with any sect or synagogue body. We can help anyone."
Younger boys are taken out for pizza or bowling sessions and never visit the centre. But for the most-troubled, this is a safe haven.
"Food is the way. We meet over a meal and can do wonders. Those who come in here on a daily or weekly basis hang out. Some boys have nowhere else to be. Why? Maybe at the moment he is off his head on drugs. We pull in favours but he might not turn up for the job interview. We need to bring some stability."
The Clubhouse was set up in 2001 in response to growing homelessness and substance abuse among teenage boys and girls. It folded eight years later when the economy collapsed, but Mr Leaman and a team of financial backers resurrected it in a disused teacher training complex.
The range of issues it deals with will shock many - drink and drug abuse and gambling.
But Mr Leaman – a father-of-four – has a series of well-developed methods at hand to help get the boys back on the straight and narrow.
Since November the club has become, bizarrely, the country's leading seller of Union Flags. It is just one strand of a thriving online retail business.
"There are guys we just can't place in work because their problems are too severe," Mr Leaman explained. "The drug addiction is too big, or they have obsessive compulsive disorder, or they can't hold down a job. So we've developed an in-house business, an eBay shop.
"The boys receive training in online selling, researching items, packaging, dispatch, customer services. Goods are donated or we buy them cheap. We network with businessmen in the community."
The team works round-the-clock to sell stock including paintings, candles and, of course, the flags.
The success of the small business is striking not only for its rapid growth, but for the range of opportunities it provides for its staff – the boys – many of whom have never previously held down a job.
Mr Leaman said: "Each boy has a different task. They have to pack the item, sort the postage and so on. We use combination stamps rather than franking so they have to weigh them and add them up and do some maths.
"We don't give up. We think differently. Some of those working on the eBay shop have achieved something for the first time in their life. That in itself is like a drug. We combat the negative drug abuse. The underlying thing with most of the kids we help is low self-esteem, and this is an antidote to that."
The Clubhouse will hold its first major funding-raising event later this month. Somewhat ironically, the gala dinner will be held at Hendon's police training college and supported by the Jewish Police Association.
Mr Leaman said: "People don't know about us. Our budget is about £230,000 a year. It's not huge, but it's money we have to raise. We get grants, from Children in Need, from the Lottery, from Barnet Council, but the rest is all private donations.
"I'm very proud. It's hard work, but we see lives changing. It's hard because we can't parade our success stories, we can't put our guys on a video. They have been integrated back into society and they don't want a stigma attached to them.
"But within the Jewish world, for a kid in trouble, we are the last stop."