Panóias Sanctuary, sometimes called Fragas de Panóias, is one of the strangest archaeological sites in northern Portugal: three large granite boulders carved with rectangular cavities and steps that were used as sacrificial altars during the late Roman period. Inscriptions in Latin and Greek identify the deities and the rituals.
The site is small — you can walk around it in twenty minutes — but unusually atmospheric, sitting on a low hillside surrounded by vineyards a few kilometres east of Vila Real. There is a small visitor centre with explanatory panels in English and Portuguese.