The clock tower in the main square is what remains of the medieval defences that once enclosed Caminha. Built in the fourteenth century as the Porta Marítima — the gate facing the river — it was raised and crowned with a clock in the sixteenth century, when the rest of the walls had begun to come down.
The granite is heavily weathered and the tower leans very slightly. You can pass underneath through the original archway, which still has the slots where the portcullis once dropped. Worth lingering for a minute on the way through.