Solo, Miradouro da Graça (Sophia de Mello Breyner Andresen) works.
The easy-living viewpoint — order a beer at the kiosk, sit under the trees and watch the light change over the castle ridge. The catch: the castle blocks part of the river view, and it fills with a young sundowner crowd. Less dramatic than Senhora do Monte just uphill, but far more comfortable to linger.