If you're looking for places to visit in northern Portugal, I'd suggest a day trip from Porto to Braga. It's around 60 kilometres north and can be reached by car, bus or train. Make sure you also venture slightly out of the city centre to visit The Sanctuary of Bom Jesus do Monte, which is one of Portugal's most photographed churches (see pictures in the lower section of the gallery below).
If you get up early you can also squeeze in a trip to Guimarães on the same day (there is a bus between Braga and Guimarães). Next: Caminha (north)