The ruins of the Castle of Almada occupy a commanding position on the cliff above Cacilhas, overlooking the point where the Tagus narrows before opening into the estuary. What survives is fragmentary — a section of medieval wall, some foundation stones, and the outlines of towers — but the site itself is worth visiting for the views rather than the archaeology. From here you look directly across to Lisbon: the old city climbing up its hills, the Cathedral visible, the waterfront laid out below.
The castle is freely accessible and the grounds are pleasant for a short walk. It is most easily reached from the top of the Elevador Panorâmico da Boca do Vento, which deposits you just a few minutes' walk away. There is no admission charge and no formal visitor facilities — just the ruins, a few information panels, and one of the best vantage points in the Almada municipality.