In between Lisbon and Porto you have around 300 Km’s of beaches that you can explore up the N109, or if you prefer you can drive up the old N 1 the road that used to connect Lisboa and Porto before the highways.
Driving north , the first cities you will find are Batalha, Alcobaça and Nazaréare three names that you might want to investigate too. In my opinion, specially Nazaré. It’s a fishing/surfing town that still keeps traditions. Batalha and Alcobaça are becoming a mandatory stop too mainly because their religious architecture Mosteiro da Batalha and Mosteiro de Alcobaça, two remaining of the Romanic style in Portugal. And also the proximity to Serra d’Aire Natural Park nice landscapes.
But if you are more interested in nightlife, beach, surf, VolksWagens’s parked on the cliffs with a nice town vibe, my favourite is Ericeira, about 40 Km North from Lisbon.
Then further north, you can choose to drive on the N1 and see Coimbra. The third oldest University in Europe. The city of students, gets a lot of events and it’s the best chance to see the unique academic traditions!