Gateway to the Mall -- no, not an indoor shopping center but one of the very grand avenues of London -- this is one of London's stateliest urban set pieces. Situated on the southwest corner of Trafalgar Square, the arch, which was named after the adjacent Royal Navy headquarters, was designed in 1910 by Sir Aston Webb as part of a ceremonial route to Buckingham Palace. As you pass under the enormous triple archway -- though not through the central arch, opened only for state occasions -- the environment changes along with the color of the road, for you are exiting frenetic Trafalgar Square and entering the Mall (rhymes with shall) -- the elegant avenue that leads directly to the palace. Tube: Charing Cross.