Lapa de Santa Margarida is a small cave chapel tucked into the base of the Serra da Arrábida, close to the water near Portinho da Arrábida. The descent is part of the visit: a narrow path and long stairway lead down from the road into a cooler, dimmer space where a simple altar sits inside the natural grotto.
It is not a grand monument, and that is the point. The place feels half devotional, half geological, with the sea just outside and the limestone cliffs above. Wear shoes with grip, take your time on the steps, and pair it with the nearby beaches or a longer Arrábida drive.