The most intriguing sight in Sesimbra is the picturesque (and often photographed) harbor, which lies against the foot of a cliff, away from the city center.
Farther down the beach, beyond the boat-clogged harbor, is the 17th-century Fortress of St. Teodósio. It was built to fortify the region against pirates. The site is not open to the public and must be viewed from outside. However, even though the fortress can't be visited, this is the town's most scenic walk, taking you along the old port, with dramatic views of the sea on one side and colorful cliffs on the other.
A walk along the ruined battlements of the five-towered Castle of Sesimbra reduces the village to a miniature. The castle encloses a 12th-century church, the oldest in Sesimbra. The site is open daily from 7am to 7pm. Admission is free.
From Sesimbra, you can head west to the headland of Cabo Espichel, with views of arcaded pilgrim hospices dating from the 1700s. The baroque interior (gilded wood and sculpture) of a pilgrimage church, the Santuário de Nossa Senhora do Cabo, can be inspected daily between 9:30am to 1pm and 3 to 6pm. Admission is free. Later, walk to the edge of the cliffs behind the church for a panoramic view of the sea. At the southern end of the Arrábida Mountain chain, this pilgrimage site has been popular since the 13th century. Modern sculpture now stands in the forlorn setting. There's no guardrail, and it's a sheer drop of more than 100m (328 ft.) to the ocean waters, so be very careful. From Sesimbra, six buses a day make the 30-minute journey to this southwestern cape.