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 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 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 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 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 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 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.

King William Street was the original terminus of the first deep level electric Tube in the world and now this station is part of the Bank upgrade project. Siddy shows Tim its Second World War shelters, original Victorian tiles and steep running tunnels and where it goes under the Thames.

Siddy also visits Knightsbridge, where old lift shafts taken out of service in the 1930s are now being put back into use to make the station accessible for all.

Tim Dunn and Siddy Holloway discover the hidden world of the Waterloo & City, the only line entirely underground. And Siddy explores abandoned Mark Lane, by the Tower of London.

Also, at the Acton depot, they rifle through the London Transport Museum's collection of unscanned photos before Tim learns about the iconic Underground moquette.

Tim Dunn and Siddy Holloway explore the disused Jubilee Line areas of Charing Cross station, now more famous as a film location. And Siddy walks the Kennington Loop while back at the depot in Acton, Tim looks at some original plans for other loops elsewhere on the network.