Guard on horseback performing the Changing of the Guard.
The Royal Palace is the setting for the Solemn Changing of the Guard ceremony on the first Wednesday of each month at 12 noon, commemorating the daily changing of the Royal Guard during the reigns of Alfonso XII and Alfonso XIII. The Changing of the Guard (taking over positions) is also held every Wednesday and Saturday from 11am to 2pm.
+ info: https://www.esmadrid.com/en/solemn-relief-and-changing-of-the-guard-at-the-royal-palace