Cividade de Terroso is a Celtic hillfort about five kilometres north of central Póvoa, sitting on a low hill with views over the coast and inland farms. The site has been excavated over more than a century and includes the foundations of dozens of stone houses, defensive walls, and a small visitor centre at the entrance.
It is the best archaeological site on this stretch of coast and reaches further back than any of the city's other monuments. Allow about 90 minutes including the small museum. Bring sturdy shoes.