Leaving Isla Canela head across the river to a place called Castro Marim to explore the castle. Castro Marim is the first town after crossing the bridge into Spain. It takes around 15 minutes to get there from Isla Canela.

The village of Castro Marim is situated between two hilltops on top of one of them is Castro Marim Castle and on the other Fort Sao Sebastian. The border with Spain and Portugal is the Guadiana river only two kilometers to the east.

The Castle has a rectangular shape with 4 round corner towers and 2 entrances. It is probably, in origin, a castle built by the Moors to protect the Portuguese coast.

The castle is located in a unique setting because of the salt flats and  the Guadiana rıver. The castle is built with red sandstone and it was destroyed by the 1755 earthquake. The high walls, which have been partly restored, shelter the ruins of an early 12C castle. The path round offers a panoramic view over the small town centre, the salt marshes, the Guadiana, the bridge which joins Portugal to Spain, Ayamonte, Villa Real de Santo Antonio and the coast in the south.