Castro Marim (Portuguese pronunciation: [ˈkaʃtɾu mɐˈɾĩ]) is a town and a municipality in the southern region of Algarve, in Portugal. The population in 2011 was 6,747, in an area of 300.84 km².
In the Roman era, Castro Marim was known as Aesuris.
Every year in the end of August there is a Medieval Fair/Festival that reunites many people from across the world to perform, like medieval musicians, archers, swordsmen, dancers, troupes, etc. There are sellers too: blacksmiths, textile crafters (weaving), herbs sellers, etc.
In honour to his Portuguese mother, Lucia Gomes, from Castro Marim, Paco de Lucía - the Spanish composer and guitarist - named his thirteenth studio album Castro Marín.