You'll never believe what lies underground in some of London's long-forgotten tube stations and abandoned WWII air-raid bunkers.
It sounds like something out of a science-fiction novel. Not even locals know it's there.
But deep beneath a bustling street in London, inside the abandoned tunnels of old World War II bomb shelters, grow rows upon rows of lush, leafy greens.
Wild rocket, radishes, basil, pea shoots and chives — the micro herbs don't see an inch of sunlight until they're picked, packaged and sent off to the city's biggest supermarkets and most luxurious restaurants up above.
The world-first subterranean farm was opened in 2015 by entrepreneurs Richard Ballard and Steven Dring, who were looking for a sustainable way to feed the city's swelling population.
The crops are grown in tightly controlled conditions and under bright pink LED lights, which Mr Ballard says gives the plants their best flavour.
"The best flavour and a good environment to work in. Very similar to daylight," he said.
"We recreate daylight and night time — so we have lights on and lights off time — and that enables the plants to rest and strengthen and grow in the perfect environment.
"We also get a consistent year-round temperature in the tunnel, which is about 15 degrees Celsius, whether it's minus five degrees or 35 degrees outside."
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The urban farm is just one of the weird and wacky ways London's decaying labyrinths of underground shelters and disused tube stations have been given new life.
For Mr Ballard and Mr Dring, the exorbitant price of land in London, coupled with its harsh seasonal weather meant going underground just made sense.
"We looked at the space that was owned by Transport for London (TFL) and they were quite intrigued by the idea. They allowed us to do a trial, which we did. We set it up and we got some good results," he said.
But other sites have proven useful in very different ways.
Highgate station, which was closed more than 50 years ago in 1962, is now a protected habitat for bats, while the old Aldwych station in Westminster is now routinely used as a film set for television shows and movies, including V for Vendetta, Atonement, Fast and Furious 6 and Sherlock.
"Inevitably when you create the first system you don't necessarily get everything right," Chris Nix from the London Transport Museum said.
The museum has just opened a new exhibition exploring the underground's eerie secret spaces.
"London's underground system is the oldest underground system in the world — it dates back to 1863 in Victorian times … but certain stations were not quite in the right place, they were technically not good enough, or operationally easy enough to use, so they became abandoned or partially abandoned."
Perhaps the most famous disused tube station was Down Street in London's up-market Mayfair.
It was used as the top-secret headquarters for the Railway Executive Committee during WWII, which was responsible for co-ordinating the transport of troops, munitions and workers across the UK. But it was also where the then-prime minister Winston Churchill and his war cabinet sheltered during The Blitz.
"At the height of The Blitz, 10 Downing Street had nearly been hit two or three times and was quite badly damaged," Mr Nix said.
"The prime minister had to move out of there (and) the war cabinet was very concerned about where he'd take shelter because they knew how vital he was to the war effort. He ended up taking refuge over a period of the next two months in Down Street station."
Far from just a dank, dark hole to hide in, Down Street was a bombproof engine room complete with typing areas, a telephone exchange, bathrooms and dormitories for the 40 staff that worked there.
It was also exempt from rations, meaning Mr Churchill was treated to an extraordinary menu of the world's best caviar, fine champagne, brandy and cigars when he visited.
"Entertainment and decent food was seen as absolutely essential to keep the morale up," Mr Nix said.
"They were drinking all the vintage stuff because the last thing you want is the invading armies capturing your fine quality cellar and drinking it for themselves."
Most of London's disused stations are now simply used for storage or as ventilation shafts to help cool the tube, which more than two million people use every day.
"That's one of the good things about these places," Mr Nix said.
"They're always useful."