The quadrangle of Windsor Castle, one of the principal official residences of the British monarch. On the far left is the State Apartments, at the end of the quad is the Private Apartments, where Queen Elizabeth II resides on weekends, and on the right, the South Wing. Located at Windsor in the English county of Berkshire, it is the largest inhabited castle in the world and, dating back to the time of William the Conqueror, the oldest in continuous occupation.Photo credit: Diliff