Postcard: London Underground

The sign says the next train is WIMBLED. What does it take to wimble a train, I wonder? Will it still run? Are there clowns at Piccadilly Circus? Druids and oaks at St John's Wood? What do they grow at Chalk Farm? Who are the Seven Sisters? The King's Cross - what made him so? Which is the Shepherd's Bush? Who is Bec, and why is she Tooting? Does the Elephant live in the Castle? Can the Angel fly?