Ponta de Sagres is the blunt headland that gives Sagres its edge-of-the-map feeling. The fortress occupies the neck of the promontory, but the wider point is about wind, cliffs, Atlantic light, and the sense that the Algarve has run out of land.
Walk it slowly rather than treating the fort as the only stop. The exposed paths give changing views toward Cape St Vincent, the harbour, and the broken coastline around Praia do Tonel. Bring a layer even on warm days; the wind here is part of the experience, and it can turn a sunny walk into something much rawer.