Horse Guards in London

The guard riding a horse in the entrance of the building

Horse Guards is a large grade I listed building in the Palladian style between Whitehall and Horse Guards Parade in London, England. It was built between 1751-1753 by John Vardy to a design by William Kent. The building was constructed on the site of the Guard House of the old Whitehall Palace, which had been destroyed by fire in 1698. The palace's tiltyard became the exercise ground of Horse Guards Parade, located behind the Horse Guards building.

The building was the headquarters of the British Army's general staff and served as the offices of the Commander-in-Chief of the British Army until the post was abolished in 1904. Horse Guards subsequently became the headquarters of two major Army commands: the London District and the Household Cavalry. The building is the formal entrance to St. James's Palace via St. James's Park (though this is now entirely symbolic). Only the monarch is allowed to drive through its central archway, or those given a pass (formerly made of ivory).

Horse Guards is always guarded by troopers of the Household Cavalry, both mounted and on foot; visiting the horses is popular with tourists. Two mounted cavalry troopers are posted outside daily from 10 am to 4 pm, and are relieved every hour. There are usually guided tours of the building on London Open House weekend, which takes place in September.
http://en.wikipedia.org/wiki/Horse_Guards_(building)