Tim Dunn and Siddy Holloway explore the abandoned branch line between Holborn and Aldwych. And at Holloway Road they find out about the Tube's only spiral escalator.

Visit one of London Underground’s most secret places: North End under Hampstead Heath. Abandoned before completion, the station became a Cold War bunker.

Explore the disused parts of Piccadilly Circus, the grandest station on the London Underground. And they also visit the long-abandoned Highgate surface station.

Explore the hidden parts of Euston, including unique features not found elsewhere and the bits set for demolition for HS2. Siddy also visits York Road station.

Have a night-time track walk exploring long forgotten stations on the District line in Whitechapel. And they discover how sprawling Oxford Circus was first built.

Explore Clapham South deep level shelter, where thousands of Londoners slept in the war. They also visit Moorgate, and the remains of a tunnelling machine there.

Tim Dunn and Siddy Holloway make their way over and explore the disused Jubilee line areas of Charing Cross station, which is now more famous as a film location.

Tim Dunn and Siddy Holloway go off and discover the hidden world of the Waterloo and City. This is the only line that is entirely underground.

Tim and Siddy visit King William Street, the earliest disused station on the deep tube. Siddy also sees new life breathed into Knightsbridge’s long-abandoned lifts.

Tim and Siddy walk the Piccadilly line at night to explore the hidden World War 2 remains of Brompton Road. Siddy reveals the unexpected wartime use for St Pauls.

Tim and Siddy explore the disused parts of London Bridge. Siddy visits Ongar in Essex, and nearby Blake Hall which, at the end, served less than 20 passengers a day.

Tim and Siddy explore Kings Cross St Pancras, including a secret siding and the disused Thameslink station. Siddy also discovers long lost Marlborough Road station.

Tim and Siddy explore the brand new Elizabeth Line – and have access to 2 of its stations weeks before the line opens. Siddy also explores the disused parts of Angel.

Tim and Siddy visit Quainton Road in rural Buckinghamshire, 50 miles from central London – and once on the underground. Siddy also explores Kingsway tramway tunnel.

Tim and Siddy visit the cathedral-like Greenwich Power Station, which stands ready to power the tube at short notice. Siddy visits hidden parts of Notting Hill Gate.

Tim and Siddy explore the tube station with the most platforms, Baker Street. Siddy visits the disused Edgware Road Signal Cabin with its very last operator.

Tim Dunn and Siddy Holloway explore the labyrinthine Camden Town station, and the forgotten wartime shelter built beneath. Plus, Siddy visits a station which hides a lost river.

Tim Dunn and Siddy Holloway explore the disused areas of South Kensington station, with platforms reclaimed by nature and wartime uses. Siddy also heads to Marylebone to reveal the original features on the platforms and the tube infrastructure hidden within the walls of a hotel.

Tim and Siddy are heading to a station you won’t find on modern-day tube maps – Dover Street, now known as Green Park. During the Second World War the abandoned passageways and lift shafts of the original station had an incredible second life as the base for the London Passenger Transport Board whose work kept London’s transport moving against all odds. Next, Siddy delves into the abandoned corridors and platforms of Down Street, closed to the public in 1932, and the scene of some of the most pivotal decisions of World War II.

Tim and Siddy embark on a night-time track walk to the abandoned station of British Museum. The pair discover enormous 1930s hand-painted adverts and evocative white tiling. During the second world war it served as a shelter and spine-tingling clues to the children who stayed there during The Blitz can still be seen. Siddy visits the elegant, white-stuccoed houses of Leinster Gardens, which are hiding a stunning secret of the London Underground behind their walls. These aren't all real houses at all, they are in fact, an incredible quirk of the Underground's history of steam.

Tube fans would be right in thinking there are 272 Underground stations on the network, but Siddy Holloway has such unique access, today she is taking Tim Dunn to the 273rd. This station only has a west bound platform, no customers and no members of the public will ever board its trains. Situated on the 3rd floor of an unassuming tower block in west London, this is TFL's state of the art training facility. Siddy also heads to one of the oldest and friendliest deep level stations at Oval. She reveals unusual brick lift shafts, surprising ventilation and the international phenomena that started life on a simple station white board. At the depot Tim explores the wild world of experimental and innovative trains and has a mind-blowing experience when he samples hot sauce, homegrown on a tube station platform.

Tim and Siddy are exploring the station in the beating heart of London's theatreland - Leicester Square. It's a place adored by tourists and culture lovers but very few know of the secrets hidden below ground. Siddy reveals the extraordinary previous life of the station office - as a display cabinet for V&A antiquities. The pair then ride what was once the world's longest escalator at 54m, explore layers of the stations design history hidden in unassuming cupboards and see the unique wartime communication infrastructure still stored in abandoned lift shafts. Tim learns more about the work to preserve the networks heritage from TFL's Ann Gavaghan. Siddy visits the tourist hot spot of Hyde Park Corner, where the stunning Oxblood Leslie Green station building has had a renaissance as a high-end hotel. She delves into its abandoned cross passages, adorned by stunning original tiles and reveals enormous fans and gloriously aging stair shafts.

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.

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 & 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.

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.

Tim and Siddy explore Earl’s Court station – a busy interchange on the Piccadilly and District lines. It’s a station that has always embraced innovation. It was the very first station to install a passenger escalator and the first to install automatic lifts. Tim discovers how even today, the station is embracing the modern, with a re-design of the walkways created to fit in with its famous glass roof. Meanwhile, Siddy visits Alperton towards the western end of the Piccadilly Line. It’s a classic example of the famous London Underground architect, Charles Holden, and the design was regarded as futuristic when it was built in the 1930s. Back at our Museum depot in Acton, a dedicated volunteer shows Tim the restored inner workings of a 1930s platform indicator, which used a telegraph system to show passengers the destination of their next train.

Tim and Siddy go under the platforms of Paddington station. It has five different tube lines running through it, with its oldest and newest lines opening 150 years apart. Tim explores a tunnel still in use under the mainline station, but with intriguing clues as to its original purpose. Siddy discovers some former police cells underneath the platforms, and unearths what remains of the luggage carousels from when passengers on the Heathrow Express were allowed to check-in their luggage in the main station. At Tottenham Court Road, Siddy reveals the huge changes to the station to accommodate the Elizabeth line, and tells the story of how the station’s iconic mosaic artwork was preserved during the works. She also takes us behind a locked door to uncover a floodgate installed as part of Britain’s Cold War defences. Back at our Museum depot in Acton, Tim meets a young tube driver who’s built up a large following on social media for her posts showing behind the scenes of her job.

Tim and Siddy explore the forgotten underground passages and tunnels underneath one of Britain’s busiest railway stations, Waterloo. Tim gets a tour of a hidden world underneath the main concourse, which includes a former typing pool, a rifle range and a full-size snooker table gathering dust. As a member of our Hidden London team, Siddy has the key to unlock a door to a secret room at the end of a Bakerloo line platform. She discovers a floodgate which would have sealed the tunnel entrance during German bombing raids over London during the Second World War. Siddy visits Marble Arch on the Central line, and meets the artist who created an iconic series of enamel artwork on the platforms in the 1980s. Each depicts the Marble Arch in a different design, and they’re still in pristine condition after 40 years. Siddy hears how the designs came about, and how the artist had to learn the intricate craft of working with enamel to realise her vision.

Explore South Kentish Town a station once on the Northern line,but abandoned more than a century ago. Tube trains still run through it, creating an eerie atmosphere and the spookiest sound they’ve ever heard in a tube station. They explore the disused passageways, reveal the ventilation shafts still working to keep air circulating on the Northern Line today, and tell the story of the passenger once stranded at the station after getting off a train by mistake. At a secret location somewhere in zone 1, Siddy gets a behind the scenes tour of the London Underground Control Centre. It’s the hi-tech mothership of the entire network, sitting in an enormous control room, running operations, power, policing and track access from one central hub. It includes a huge multi-screen display, which can show simultaneous live feeds from any of the 12,000 CCTV cameras on the underground. Tim meets one of the underground’s buskers to hear the secrets to her craft

Tim and Siddy reveal the incredible story of the Thames Tunnel – the first successful tunnel built under a major body of water anywhere in the world. It was built by Brunel and his father – and not originally intended for trains - but today links Rotherhithe and Wapping stations. Tim hears about the incredible engineering that made the tunnel possible – as well as the many failed attempts to get it right, including a major flood. Siddy walks the tracks in search of evidence of the tunnel’s original construction, revealing a series of striking arches. In Lambeth North, Siddy explores this classic Leslie Green station, one of the least used in zone 1. But it has a significant history as a shelter during the Second World War, and as a training base for London Transport workers, especially women drafted in to work on the tube during the war.

Tim and Siddy get privileged access to the vast maintenance depot at Ruislip, at the end of the Central line. It’s the nerve-centre for all that takes place on the tube, from routine track repairs to emergency engineering. Tim gets a demonstration of how tracks are replaced, as a crane lifts huge pre-assembled sections of railway track into place. Siddy gets in the driving seat of a machine that moves ballast into place under sleepers to hold the track in position. At Warren Street, on the Northern and Victoria lines, Siddy explores the station’s constant reinvention. It first opened in the early 1900s, was remodelled in the 1930s and then had a massive make-over in the 60s when the Victoria line arrived. At the Museum depot in Acton, Tim meets a poet who has had her work chosen to appear as part of the ‘Poems on the Underground’ series.

Tim and Siddy get access to the maintenance depot at Northumberland Park, responsible for looking after the entire fleet of Victoria Line trains. Tim meets the team checking all the carriages, and sees the incredible precision needed to finely shave the metal wheels to keep them running smoothly on the tracks. Siddy checks the vintage control panel on the tower and finds it is still in working order. They ride on the private service that links the depot with Seven Sisters station alighting at its mysterious third platform. At Finsbury Park station on the Victoria and Piccadilly lines, Siddy does a night-time track walk to access the now-disused tunnel which was part of an early experiment to run large electric mainline trains on the tube. At our Museum Tim hears about the importance of design across the tube network, and looks at the bespoke designs for seating fabric across different underground lines.

Explores the rich history of Stockwell station on the Victoria line. It was originally the terminus station for the City and South London Railway – the first ever deep level electric tube railway in the world, and the birth of the tube as we know it. Tim finds evidence of a deep level shelter used by Londoners during the Second World War. On the platforms, he reveals something rather more contemporary – the tiles depicting a swan in homage to a local pub. As Siddy descends deep into the station, she finds metallic tiles on the walls and cast iron segments in a disused lift shaft, each crucial relics of their era. Siddy visits the main depot for the DLR. She hears how they’re developing new technology to alert them to any passengers on the tracks. And she gets a preview of their new fleet of trains currently on test runs along the network. At the Museum depot, Tim explores the items in their collection charting the history of the DLR, including models of the original 1986 trains.

Tim and Siddy meet at Gloucester Road in London’s museum quarter – a station serving the Circle, District and Piccadilly lines. It was built as two separate stations, with the earliest, grander section opening in the 1860s. Tim finds an original footbridge still overlooking the modern platforms, as well as a hidden space where you can still see the brickwork of the early tunnels. Siddy explores the later station – a Leslie Green design built in the early 1900s with original tiles and remains of the lifts still in evidence. Tim and Siddy also explore the now-disused platform that’s been turned into an art gallery. Siddy leaves London to visit Goole in Yorkshire where 70 new Piccadilly line trains are being assembled. She gets a tour of the factory and is allowed on board a new open-plan carriage, being fitted with air conditioning.

Explores the unusual station at Old Street. It serves both the Northern line and mainline trains, and they discover how the platforms and tunnels differ across the two different services. The station has undergone massive changes since it first opened in 1901, and there’s still plenty of evidence of its early years, if you know where to look. Tim goes through a tiny doorway to discover a hidden passage with an original fully-tiled vaulted ceiling. Siddy discovers a staircase last used in the 1920s, which still has the original sign showing the Northern Line tube stops. Siddy visits Hampstead, the deepest station below ground on the entire Underground network. Unsurprisingly, it also has the deepest lift shaft, and she gets to ride on top of the lift to see the record-breaking 55-metre shaft up close. At our Museum depot, Tim meets the first ever female driver on the Victoria line. She talks about working on the tube in the 1970s.