No 11 Bus

Finally not strictly free but still a bargain if you have a travelcard, the No 11 Bus goes past many of London's top sights. The route starts at Liverpool Street and goes past St Paul's Cathedral and along the Strand to Trafalgar Square (for the National Gallery), down Whitehall past Horseguards and Downing Street to the Houses of Parliament and Westminster Cathedral, on to Victoria and the shops along King's Road in Chelsea.