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.