Three days covers Porto on both banks: old city, Gaia and Foz

Day 1: São Bento, the cathedral, Clérigos, then down to the Ribeira

Day 2: walk the bridge to Gaia, port lodges, sunset at Jardim do Morro

Day 3: Tram 1 to Foz and a walk to the Felgueiras lighthouse

Or swap day 3 for the train to Peso da Régua, about two hours

Rain day? Move Gaia there: the port lodges are indoors

Walk down, ride up: both day-by-day plans are in the guide