As you enter town through the massive, arched gates of Óbidos, it seems as if you've been transported to Portugal in the Middle Ages, when the fortress was taken by Portugal from the Moors. The narrow Rua Direita, lined with boutiques and white, flower-bedecked houses, runs from the gates to the foot of the castle: you may want to shop for ceramics and clothing on this street. The rest of the medieval-era village is crisscrossed by a labyrinth of stone footpaths, tiny squares, and decaying stairways. Each nook and cranny offers its own reward. Cars aren't permitted inside the walls except to unload luggage at hotels. Parking is provided outside town.
Away from the walled town, two pleasant marked walks enable you to see some rural history and Roman ruins or visit a bird observatory, respectively. It's a 1-km (½-mile) trek from the city gate through farmlands, a grove of poplar trees, and along the Arnoia River to the Eburobritium Roman ruins (established 1 BC to AD 5), where you can see ancient baths and a forum. Another walk is out to the free Lagoa de Óbidos observatories, from where you can spy aquatic birds and birds of prey. Maps of Óbidos are available at the tourist office in the parking lot at the gate into the city wall.
Once a strategic seaport, Óbidos is now high and dry—and 10 km (6 miles) inland—owing to the silting of its harbor. On the approach to town, you can see bastions and crenellated walls standing like sentinels over the now-peaceful valley of the Ria Arnoia. It's hard to imagine fishing boats and trading vessels docking in places that are today filled by cottages and fields.