Horse Guards Whitehall is a large very grand building between Whitehall and Horse Guards Parade. It is the headquarters of two major Army commands: the London District and the Household Cavalry, and is guarded by sentinels during the day in the two sentry boxes each side of the entrance.
The passage under the Clock Tower leads to St. James's Park and Buckingham Palace. At the Horse Guards Parade, the ceremony of Trooping the Colours on the Queen's Birthday is held.