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 and Siddy are heading to a stunning 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 essential work kept London's transport moving against all odds. Next, Siddy delves into the atmospheric, 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.