14 July 2016 Last updated at 08:26 BST
Deep underground the biggest building project in Europe is taking place, to make a brand new underground railway line.
The project to build this new trainline for London started in 2009, with lots of digging.
Builders even unearthed skeletons dating back to Roman times, roman coins and roads, a tudor mansion, and a plague pit.
Seven new stations are expected to open in 2018, with 200 million passengers set to use the new line every year.
CBBC's super scientific reporter Fran Scott has gone 'under' the scenes to find out what goes into this massive build.

Marilyn Carre was giving evidence at an inquiry investigating claims of abuse in the care system dating back to 1945.
The inquiry also heard Ms Carre describe the Haut de la Garenne children's home as a "barbaric" place.
Ms Carre joined Children's Services in 1977 before becoming a probation officer in 1990.
Ms Carre explained how, while serving as a probation officer, she had visited Les Chenes secure school to see a client who had been locked up and was screaming, apparently coming down from heroin.
She told the inquiry she reported concerns to her superiors and was told a doctor had been called, but weeks later, the girl told Ms Carre she had been in agony and had not seen a doctor.
Ms Carre, whose career took her to most of Jersey's children's homes in the 1970s, 80s and 90s, described Haut de la Garenne as a "barbaric" place by today's standards, where violent teenagers were kept with younger children.
The former social worker also said Morag Jordan, who worked at the home and was later convicted of abuse, was "cold as ice" and added that she used to pin children against walls.
The independent inquiry began in 2014 and Chief Minister Ian Gorst has set a deadline of December 2016 for it to conclude its investigations.

The Nottinghamshire born athlete, who is a double amputee, set off from John O'Groats in August and headed into Land's End on Monday.
The 37-year-old 200m sprinter, who began his career as a marathon runner, said the task had been five years in the planning.
He said the challenge had been "an epic journey".
"I'm really tired. It has been really tough the last couple of days," he said.
"Cornwall is really hilly and the energy levels are wacked at the moment. But I have had a great team around me who have supported me.
"It has been awesome to see people on the way and the support online as well."
Richard Runs Britain has raised £105,000 for charities Sarcoma UK and Scope, considerably less than his £1m target.
He asked people to run with him at certain points and was joined by several athletes and celebrities along the way.
Whitehead said he had been inspired by amputee and sarcoma cancer sufferer Terry Fox, who attempted to run across Canada in 1980.
He added: "Unfortunately he didn't reach his destination but he inspired me to start running myself and after last year's success at the Paralympics I got this once in a lifetime opportunity up and going, and here we are."
Before his challenge Whitehead said he had wanted to reach out to people of all ages and abilities and encourage people into sport as part of the legacy of the Olympics and Paralympics.
He was joined for the last two days of the journey by his wife and seven-month-old daughter.
Something BIG is happening beneath the streets of London.
[NEXT_CONCEPT]
Concerns over the treatment of children at Jersey's care homes were either covered up or ignored, according to a former social worker.
[NEXT_CONCEPT]
Paralympic gold medallist Richard Whitehead has completed 40 marathons in 40 days.