The Fort of Santo António sits at the mouth of the Gilão River where it meets the sea, about 3 km south of the town at the Quatro Águas dock. The seventeenth-century fortification was built to guard the river entrance and the tuna fishing operations that were Tavira's economic backbone for centuries. The fort is small and access is limited, but the exterior is visible and the surrounding area at Quatro Águas is pleasant for a walk.
The dock at Quatro Águas is also the ferry point for Tavira Island and has several seasonal fish restaurants with views across the lagoon. The combination of fort, ferry, and fish makes the area a worthwhile half-afternoon from the town centre.