Castro Marim is a village with a history that makes it worthy of a visit. At the top of a hill stands the Castle; on another, the modern fort, with a system of large curtains and extensive bastions. Whitewashed houses of colourful parapets, roof terraces and laced chimneys spread out between the two fortresses. Around the visitor, horizons of mountains, river and sea extend in all their grandeur.
The walled fence that used to surround the medieval village on the top of the mountain dates from the 13th and 14th centuries. On the large terrace, inside the fence, stands the Old Castle, built in 1274 by D. Afonso III, as evidenced by the tombstone placed over the door which leads to the inside. It features a square shape with circular turrets at the corners and on the two doors. There is a curious relief in form of a key and acronyms that were typical of medieval stonemasons.