The viewpoint at Graça, on the hill above and behind the Alfama, offers one of the best views in Lisbon and is significantly less crowded than the famous Portas do Sol viewpoint below. From here you look across the terracotta rooftops of the Alfama to the Castelo de São Jorge on the adjacent hill, with the Tagus visible beyond.
The square below the viewpoint has a café with outdoor seating that fills up at sunset. The Graça neighbourhood surrounding it is one of the most authentic remaining areas of the old city — steep streets, local shops, few tourists. Take tram 28 or bus 734 from the centre; the tram is more scenic but always crowded.