Tim and Siddy explore the forgotten tunnels underneath one of Britain's busiest 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. Siddy 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.And at the depot of the London Transport Museum, Tim learns about the latest enamel signs still being made and used across the Underground network, including the signage for the new Windrush Line.