Looking like an unassuming alley but barred by iron gates at both its Whitehall and Horse Guards Road approaches, this is the location of the famous No. 10, London's modest version of the White House. Only three houses remain of the terrace built circa 1680 by Sir George Downing, who spent enough of his youth in America to graduate from Harvard -- the second man ever to do so. No. 11 is traditionally the residence of the chancellor of the exchequer (secretary of the treasury), and No. 12 is the party whips' office. No. 10 has officially housed the prime minister since 1732. (The gates were former prime minister Margaret Thatcher's brainstorm.) Just south of Downing Street, in the middle of Whitehall, you'll see the Cenotaph, a stark white monolith designed in 1920 by Edwin Lutyens to commemorate the 1918 armistice. On Remembrance Day (the Sunday nearest November 11, Armistice Day) it is strewn with red poppies to honor the dead of both world wars and all British and Commonwealth soldiers killed in action since; the first wreath is laid by the queen and there's a march past by war veterans. Tube: Westminster.