They're not exactly regular tube users, so commuters were rather surprised to see Prince Charles and The Duchess of Cornwall underground this morning. The Royal couple swiped in using their own oyster cards, like the rest of us, but their journey was anything but average, as Rags Martel reports.
A steam train which carried passengers in the 19th Century has returned to mark 150 years since the first tube journey.
A look back at some of the stops on London Underground's 150 year journey.
All day we've been adding fascinating facts about the Tube, which turns 150 years old this week. Now find out how much you know.