Changing of the guards take place every last Friday of the month at 11 a.m. (except July, Aug, Dec).
Wikipedia (Spanish) http://es.wikipedia.org/wiki/Palacio_de_Buenavista_(Madrid)
More information at esmadrid.com http://www.esmadrid.com/en/tourist-information/palacio-de-buenavista
地址 Calle de Alcalá, 51 28014 Madrid, Spain
坐标 40°25'16.169" N -3°41'41.809" E
