Porto is quite a haul from Lisbon so its a curious choice. On the way is Coimbra which is where Coimbra university is. This university was started in 1290 and has a fantastic library. IIRC, it is the third oldest university in the world. Nazare is a nice beach and a nice fishing/touristy town.
I don't believe you are religious, IIRC, but Fatima is also north of portugal. Fatima is where three kids saw Mother Mary. It is fascinating even if you are not religious....people make pilgrimages there and the people watching, along with the temple, are very much worth the trip.
Palacio Naional de Sintra is on the UNESCO list of sites so its pretty cool.
Here
is a decent site.
I am interested in why you are going north instead of south from Lisbon. South has some great resorts and golfing...perhaps one of the best and most under rated places to vacation in Europe. Just check out Algarve...google it.
You bring back memories...I was in Lisbon, really a small place named Sao Martinho. There is a bay which is great for swimming. We camped on the hills overlooking the ocean and scraped off muscles to fry for breakfast. It is a beautiful small fishing village. The guy who took me, then we went to college together, was from Portugal and I sponsored him for his US Citizenship. He ended up being the lead engineer on the Navy's Rail Gun project (now being deployed) so I feel I made my contribution! He was also, BTW, our small college's Field Goal kicker. He was 23 for 23 on extra points and 10 of 11 on FG's as a true freshman. He was one of the first soccer style kickers in college ball. He had pro capabilities but in the spring, he had a conflict with an engineering lab and spring practice. the coach wouldn't excuse him for lab so he quit football and never went back. Back in the day, you were expected to change majors for football. A shame.