Thames Tunnel: Rare access to 'eighth wonder of world'
The Thames Tunnel was once known as the eighth wonder of the world.
In Victorian times, hundreds of thousands of Londoners flocked to see it - amazed at how they were able to walk beneath the river.
However, since becoming part of the East London Line, the public rarely get a chance for a close-up look at the Brunel engineering masterpiece.
But this weekend, with the London Overground closed for upgrading works, Transport for London opened the tunnels to the public.
BBC London's Charlotte Franks was one of the lucky ones to get a guided tour.