Secrets of the London Underground

Tim Dunn and Siddy Holloway pack their bags to go on a trip around the sprawling Heathrow Airport underground stations - the first ever underground rail link between an airport and a city. They start their trip at the original Heathrow Central, now Heathrow Terminals 2 and 3, stopping off at Hatton Cross, with its eye-popping 70's mosaic tiling and speedbird logos, before they finally reach the futuristic 80's design of Terminal 4. Finally, they embark on a special trip along the Heathrow loop, the tube tunnel link which passes underneath the runway. Climbing through the driver's cab, they alight at a secret platform to explore a ventilation shaft and emerge above ground to the sound of aircraft.

Next, Siddy heads to north west London to delve into Swiss Cottage station, one of the first stations to be built on the expanding Metropolitan Railway. With those original platforms closed to the public 80 years ago, she explores what remains of that forgotten world.

At the museum Tim has a ride on an Elizabeth Line train simulator and at the depot he meets contemporary artist Mark Wallinger who created the ubiquitous labyrinths which adorn the walls at 270 Underground stations.

Shepherd's Bush is a fabulous example of how the network has changed and adapted over time and Siddy Holloway knows where all the best bits are, ready to show Tim Dunn. Just off the platforms the pair discover Victorian glass tiles, long abandoned passenger tunnels from the original Central London Line, epic vents with an eye-level view of people on the platforms and a lift shaft with an escalator through the middle. They visit a gigantic cavern hidden within the body of the station and the perfect example of how nature sometimes beats the best laid engineering plans.

Siddy delves into Elephant and Castle, a small station that packs a big punch. She discovers what it takes to be at the helm of a train from driver Jennifer, reveals the only original 1890 tiles still visible to the public and the spooky discoveries hidden behind a platform door.

At the depot Tim hears about one of the most captivating parts of TFL - the Art on the Underground programme and has the time of his life with Assistant Director Chris Nix as they rev up the special road and rail vehicle currently being restored by the museum.

Tim Dunn and Siddy Holloway explore the sprawling TFL maintenance facility - Acton Works. Staying in Acton, Siddy reveals an oddity of Underground history.

Tim Dunn and Siddy Holloway have access to the secret spaces of Archway, from cavernous lift shafts to sealed off tunnels. Siddy also visits the tube's own Emergency Service.