The Alcázar of Seville (Reales Alcázares de Sevilla) is one of the most-visited sites in Seville. It’s a stunning palace built for Peter of Castile in the 14th century and a brilliant example of Mudéjar architecture, as well as being the oldest royal palace still in use in Europe. The site can get busy during the peak tourist season, and lines for tickets can be long, so book yours in advance to save time on the day!