Not all tube stations are born equal.

Some, like Mill Hill East, are reached by soaring viaducts, carrying the tracks a reasonable 60ft above ground level: Dollis Brook Viaduct, which leads to the station, is the highest point on the London Underground. Others, like Westminster, harbour vast cavernous halls with escalators plunging ever further into the depths of London.

Given that it’s called the London Underground, the startling thing is that it’s not actually underground all that much. Only 40 per cent of is actually below ground, and only two lines – the Victoria and Waterloo & City – are entirely below ground.

Others, such as the Metropolitan and the District, only spend a relatively short proportion of their lifespan underground, with vast expanses stretching out into the west, north-west, and east of suburbia.

So, it begs the question. On the world’s oldest underground railway system, which station is the most… underground?

As ever on CityMetric, this very quickly denigrates into an argument about the terms of the question – so it makes sense to run through all the different possible answers.

Firstly, the answer nobody sensible would think to want: how far above sea level the entrance to the station is.

West Ham, which is not near Hampstead. Image: Richard Rogerson.

By that measure, West Ham is the ‘deepest’, with the station entrance sitting just one metre above sea level (come friendly global warming, and raise sea levels on West Ham). This is something of a theme on the Jubilee Line Extension, as Bermondsey, North Greenwich and Canning Town all follow behind at two metres above level: no surprise, perhaps, given that trains struggle with steep gradients.

But onto more important things. If you take the average depth below sea level of all the platforms in each tube station – an important clarification – London Bridge comes out on top (bottom). Its platforms are, on average, 22 metres below sea level.

Highly candid shot of London Bridge's platforms. Image: Zverzia.

On average, Southwark follows at 21 metres, Elephant & Castle at 18 metres, followed by Pimlico at 16 metres below sea level on average.

But seeing as some stations have very shallow platforms on lines like the District and Circle, alongside very deep platforms on lines like the Central – think of the annoyance of changing at Notting Hill Gate or King’s Cross St Pancras – the average depth in one station probably isn’t all that useful.

Which brings us to the deepest single platform.

The eastbound and westbound platforms of the Jubilee line at London Bridge make a good showing, with both coming in at 23.2m below sea level.

Southwark, just next door, makes an effort, but can’t really compete at 20.5m below sea level on its two Jubilee line platforms.

The majesty of Westminster. Image: Voyager.

Common knowledge, and Google search, has it that Westminster has the tube’s deepest platform – but according to TfL’s own figures that’s not the case.

While the westbound Jubilee Line platform at Westminster is very deep – at 25.4m below sea level – it’s beaten to the top (bottom) spot by Waterloo next door.

Both the eastbound at westbound Jubilee platforms at Waterloo are 26m below sea level – again, disclaimer, as per TfL’s own official figures – making them the deepest tube platforms on the network. If you want to nerd out at the whole data set, you can access it here.

But again, with conjecture being the order of the day – who really cares how far below the sea the tube is?

We’re Londoners, not softies of the South Coast. We don’t care about the sea. We haven’t seen the sea for years.

What we really want to know is how far below ground level the tube is – a question that renders a completely different result.

A historic shot of the deepest tube station. Image: Ben Brooksbank

And with no ado about something, the answer there is Hampstead.

Because the northern line station there sits on the picturesque but thigh-aching Hampstead Hill, the tube platforms may not be that far below sea level but they are an awful long way below the ground.

The southbound platform is about 0.8m deeper than the northbound platform, according to TfL figures, but they’re both about 58.5m below ground level.

So there you have it. The more you know.

Jack May is a regular contributor to CityMetric and tweets as @JackO_May.

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