But for those who know where to look, a second entrance reveals a hidden staircase that spirals even deeper down into the ground.
At the bottom, lies a sprawling labyrinth of gloomy tunnels, each 16 feet high and 400 metres long.
These are the station’s eight deep level shelters, built during World War Two to protect Londoners from Nazi air raids.
Commissioned by the Government during the Blitz, the shelters were completed within 18 months, but only opened to regular Londoners in 1944 with the advent of the V-1 flying bomb.
Capable of housing up to 8,000 people overnight, the tunnels were fitted with bunk beds stacked three high, canteens, a medical unit and toilets.
Seven of these shelters were built under Northern line stations, as well as an eighth under Chancery Lane.
Construction was carried out by London Transport, the precursor organisation to Transport for London (TfL), who were enticed by the prospect of repurposing the tunnels after the war for its network.
At one time, there were plans to connect all of the deep level shelters to form a new ‘express’ Tube service under the Northern line.
Travelling the same route as existing services, these trains would have been bigger and called at fewer stops.
This vision was ultimately never realised but the shelters at Clapham South can still be visited today, through the London Transport Museum’s ‘Hidden London’ tour.
Guided by a costume actor in Civil Defence warden uniform, tourists are walked through the history of the tunnels from construction to the present day.
Here, they learn that although conditions were demonstrably cramped, the shelters were first advertised in the 1940s as “luxury tunnels”, with amenities including “comfortable canteens”.
For the modern visitor, the tunnels feel eery and claustrophobic, the silence briefly punctuated by the low rumble of a Northern line train passing overhead.
And it is hard to imagine that the space felt more homely for those who sheltered in them 60 years ago, packed into the shelters with thousands of other terrified Londoners, the air heavy with cigarette smoke.
Many were forced into the tunnels out of necessity rather than choice, having nowhere to stay after their homes were destroyed by bombs.
One such Londoner was Margaret Barford, whose house in Sarsfield Road, Balham, was flattened by a V1 rocket when she was just ten years old.
She spent the next two years with her family in Clapham South’s deep-level Tube shelter, living shoulder-to-shoulder with others whose lives had been upended by war.
Despite the difficult circumstances, in an oral history played out loud to visitors, Margaret reminisces fondly about her time in the shelter.
“I had a wonderful time,” she explains. “I was an only child, and I made friends. We used to rush up and down the tunnels.
“People were all in the same boat down there. It was a great leveller. Whether you were rich, poor or whatever you were. If you were homeless.
“People were very kind to each other, much more than they are now. It’s funny isn’t it, that it takes a war to do that.”
After the end of the conflict, the shelters continued to be used as cheap hotel accommodation costing three shillings a night, equivalent to £4 today.
Guests at Clapham South included those who arrived in Britain from the Caribbean as part of the Windrush Generation.
But in 1956, after a fire at the Goodge Street station shelter, the Government decided to abandon the tunnels.
Today, they are mainly used as archive storage, although the tunnels under Clapham Common once housed a hydroponic farm.
For anyone who wants to check out the shelter themselves, new dates for the ‘Hidden London’ tour were released earlier this week, with tickets costing £38.
