When you take a moment to think about it, the London Underground is an absolute modern marvel.
It allows for well over a billion journeys each year by people each year - all without clogging up London's already busy streets.
But when work first began to assemble the great underground railway more than 150 years ago, it operated in a totally different way. For a start, there were no electric trains.
Back then, steam trains served the first lines - and they have still left their mark on the city.
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For someone walking down Leinster Gardens in Bayswater who didn't know what they were looking for, would notice nothing amiss with numbers 23 and 24.
Despite the buildings appearing the same as their neighbours the windows betray they're not.
Rather than glass, with rooms behind them, from the street you see just painted plaster.
In fact, it's not just the windows that are fake but the whole building. Number 23 and 24 are fake houses. They are just facades to match their neighbours.
Behind this is an exposed section of the Metropolitan line.
This bizarre ruse was to cover a very necessary part of how Underground trains ran in the late 19th Century.
Steam trains served the Metropolitan Line which runs beneath Leinster Gardens and was fueled by coal.
Despite clever contraptions called condensers, which stopped the tunnels filling with smoke, the engines needed to release the fumes somewhere.
That's why you had open-air sections.
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Here the driver could vent off the smoke and condensation that had built up in the long underground stretches.
Because Leinster Gardens was such a posh part of town, the people building the railway didn't want the character of the street changed.
Instead the facade was built to hide machinations of the Metropolitan Railway (later became the Metropolitan line) that ran beneath them.
If you walk down Porchester Terrace, the next road along from Leinster Gardens, you can see the back of the facade and the open section of railway.
It also shows how the line was built.
The tunnel is just below the surface because it was built using the 'cut and cover' method, where a trench was dug and the railway sunk into it.
Then the 'cap' would be built over the top covering the tunnel and allowing further buildings to be put up.
The Metropolitan, District and Circle lines were all built with this technique.