Six lucky cyclists have ridden London's deepest bike ride nearly 200 feet below the surface inside a 2.8 mile-long super sewer.
The tunnel is between 40 and 50 metres below ground.
Construction of the sewer began in 2016 and is set to be completed in 2025.
When finished, the super sewer will remove 95 per cent of around 40 million tonnes of raw, untreated sewage that currently spills into the river Thames every year.
The new system will provide a cleaner environment for wildlife and recreational river users.
Employees working on the project at Tideway London were offered the opportunity to buy raffle tickets to win the chance to take their bikes down into the depths.
In total, 360 raffle tickets were bought, raising £1,535 for charity.
The group made their descent underground in Battersea, emerging at Blackfriars.
Despite being far below the London skyline, home comforts weren’t amiss.
Instead of a dank and dark space they were met with a bright and warm tunnel.
The sheer size of the sewer made it feel like a giant hall rather than a sewage system, and its earthy smell reminded those down there of a country walk.
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To add to the luxury there was even Wi-Fi.
The eager cyclists were squeezed into a crate and lowered into the tunnel via a crane.
The journey down took around two minutes before they landed on the sewer floor.
The atmosphere was one of excitement amongst the cyclists, who found it surreal to hear the sound of the tube as it rushed above them as they cycled to Blackfriars and back.
The tunnel slopes up from Battersea to Blackfriars, with its deepest point hitting 66m below ground level.
Taylor Geall, media relations manager at Tideway London, explained: “The event went really well and everyone had a really good time.
"It’s a once in a lifetime experience.”
The project is still on track to keep within its budget of £4.4 billion.
The tunnel has been paid for by Thames Water customers, who pay between £20 and £25 each year for the project.
Taylor said: “There has been a desire for many years to clean up the river.
“The sewer system in London is 150 years old and is miraculously still in a really good condition but it just can’t cope with the modern day population of London.
“A lot of analysis was done in the 90s to find out what the best solution would be and this super sewer was chosen as the quickest most cost effective way of cleaning up the Thames.”
The team are now over 85 per cent of the way through, making their 2025 goal start to feel like a reality.
The raffle raised money for the charities Time & Talents and the Felix Project.
Time & Talents is a community centre in London, while the Felix Project saves surplus food and distributes it to charities that help those in need.
Taylor added: “We’ve had staff charity partners since we started work in 2016 and they always go down to a staff vote.
“What we look for in charities is that they are London based as we’re a London project and that they benefit local community.”
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