Secret passageways

Some that I have come across in London:

• Cockpit Steps/Birdcage Walk, Westminster - charming
• Victoria Road/Kynance Mews, South Kensington - pretty
• Ennismore Street/Rutland Street, Knightsbridge - surprising
• Vineyard Mews/Houblon Road, Richmond - useful (to me :-)
  

However, the City really has them all beat; take this outstanding walk to see why.

Update - The guide to alleys, courts, passages and yards of central London!