Each year, with almost no exceptions, the British Sovereign (King or, as presently, reigning Queen) celebrates His/Her 'official birthday' (which is held on a chosen Saturday in Spring, regardless of H.M.'s actual birthday) by attending arguably the most elaborate annual display of military parade skill. Each year one of the infantry regiments of the Royal Guards (the Grenadeers, Coldstream Guards, Scotch Guards, Welsh Guards and Irish Guards) gets its turn to star its 'colours' (regimental flag) in an elaborate ceremonial on the parade ground near the London Cenotaph, which also involves the mounted Horse Guards and the arrival from and return to Buckingham Palace in coaches of most of the royal family, except for the Royal Colonels who participate on horse-back themselves.
