10 things to know about the London Underground

Most Londoners experience the Tube as a queue, a draught of warm air and a voice telling them to move down inside the carriage. Underneath that daily grind sits the oldest underground railway on the planet, a network that is only about half underground, and a set of records nobody would design on purpose.

Here are ten things worth knowing about the London Underground, all of them checkable, none of them the sort of thing a tourist leaflet bothers with. The station and line data quoted here is the same set that powers our London guessing game and the network explorer.

1. It opened in 1863, and the first passengers travelled behind steam engines

The Metropolitan Railway opened to the public on 10 January 1863, between Paddington and Farringdon Street. It was the world's first underground passenger railway, and it carried 9.5 million people in its first year, in wooden carriages hauled by steam locomotives through tunnels dug by cut and cover. The engines burned coke and later coal, and the ventilation was, by every contemporary account, terrible.

Bits of that first railway are still in daily use. Platforms 5 and 6 at Baker Street, now Circle and Hammersmith & City platforms, date from 1863 and have been restored with the original ventilation shafts lit up, so you can see roughly what the place looked like before the smoke cleared.

2. Only about 45 per cent of the Underground is actually underground

Of the 402 km of route on the network, Transport for London reckons only around 45 per cent runs below the surface. Everything past Finchley Road on the Metropolitan, most of the Central line in Essex and vast stretches of the District are ordinary open-air railway with an Underground roundel bolted onto the platform. The 272 stations in the current network include a good number where you have never once gone down a set of stairs.

3. The deep tunnels are 3.56 metres across, which is why the trains look like that

There are two entirely different railways here wearing the same badge. The sub-surface lines (Circle, District, Metropolitan, Hammersmith & City) were dug from the street and take full-size carriages. The deep tube lines were bored, and the standard tunnel is about 11 feet 8 inches, roughly 3.56 m, in diameter. Every curved ceiling, every seat you cannot sit upright under at the end of a Bakerloo carriage, follows from that number.

4. Hampstead is the deepest station, because it sits on the highest hill

Hampstead's platforms are 58.5 m below ground level, the deepest on the network, and its lift shaft, at around 55 m, is the deepest too. The reason is topography rather than ambition: Hampstead village is on some of the highest ground in London, and the Northern line tunnels had to pass under the hill at a constant gradient. There are no escalators. If the lifts fail there is a spiral staircase of roughly 320 steps, and the signs warning you off it are not being dramatic.

5. The Northern line holds the longest continuous railway tunnel on the network

From East Finchley to Morden via Bank the train stays underground for 27.8 km, about 17.25 miles, through 25 stations and roughly 50 minutes of daylight-free travel. It was bored in stages between 1890 and 1939 and was for decades the longest railway tunnel in the world. Nothing about the journey feels like a record attempt, which is rather the point.

6. Angel has the longest escalator, and it is not close

The escalator at Angel is 60 m long with a vertical rise of 27 m. It exists because the station was rebuilt in the early 1990s to escape a genuinely dangerous island platform on the Northern line, one so narrow that staff had to control crowds at rush hour. The fix was to bore a new southbound tunnel, hand the old one over to northbound trains alone, and connect the whole thing to the surface with the tallest escalator anyone has managed to fit under Islington.

7. The Waterloo & City is two stations long and physically cut off from everything

The Waterloo & City has exactly two stations, Waterloo and Bank, sits entirely in tunnel, and has no track connection to any other railway. Rolling stock has to be craned in and out through a shaft at the Waterloo end. The whole line is about 1.5 miles and takes roughly four minutes. It opened in 1898, it runs for commuters rather than tourists, and City workers have called it the Drain for well over a century.

8. The network reaches deep into Buckinghamshire, and it shows in the records

Amersham is the highest station above sea level on the whole system, 147 m according to TfL, and also its most westerly. The longest gap between two adjacent stations anywhere on the Underground is on the same branch: 3.89 miles, about 6.26 km, from Chalfont & Latimer to Chesham. This is the leftover of Metro-land, the estate-and-railway project the Metropolitan Railway ran in the early twentieth century, building houses in the Chilterns and then selling season tickets to the people who bought them.

9. The famous map is not a map

Harry Beck's diagram first appeared in 1933. It throws away geography, straightens everything to 45 and 90 degrees, and stretches the middle so central London is legible. It works brilliantly for deciding where to change, and it lies constantly about distance. Leicester Square to Covent Garden on the Piccadilly is the classic victim: 260 m of tunnel, quicker to walk, and roughly the most expensive stroll in London if you pay for it.

10. The gap between the busiest and the emptiest station is comical

The Underground carried 1.216 billion passenger journeys in 2024/25. In the data behind our game, the two busiest stations are Waterloo and King's Cross St Pancras at roughly 77 million entries and exits each. At the other end, Roding Valley on the Hainault loop of the Central line recorded around 170,000 in 2024, the lowest on the network. Waterloo gets through Roding Valley's entire year in about a day.