Mosteiro da Serra do Pilar

Crowning the Gaia heights across the Douro from Porto, this Renaissance monastery is unusual for its circular church and matching round cloister, a rare plan in Portugal inspired by classical models. Built in the late sixteenth century, it later served as a military stronghold during the nineteenth-century siege of Porto, its terraces commanding the river crossings. The wide viewing platform outside offers a celebrated panorama of the old city, the port cellars and the tiered iron bridge, and it forms part of the UNESCO-listed area.