Advice for coastal towns between Porto and Lisbon

We had lunches in Nazare by the beach and in Aviero. Nazare was touristy but once were in a nice restaurant we enjoyed our seafood lunch and sea view. A little north of Porto is Viana do Castelo which I recommend for a stay.

On my scouting trip before moving here, I stayed in São Martinho and enjoyed it. It’s quiet and has a nice beach and a number of good restaurants. You really do need a car, but driving in the area is very easy with good signage. This was before the days of me using Google maps and I was able to navigate to Alcobaça, Batalha, Obidos, Caldas da Rainha and Nazaré without difficulty.

Biking to these places might be a bit tricky because the roads are pretty narrow and there are no broke lanes. But, it’s relatively flat so would be doable.

Thanks Suki and Kathryn,
I forgot to ask about how we would get from Porto to Sao Martinho? I guess we would need a car? Would we also drive from Sao Martinho to Lisbon and then drop it off there? Or is there an easier alternative?

São Martinho do Porto (is it the right one?) has a train station, so you do not need a car to get there.
It would be helpful for day trips, but perhaps not essential, depending on your goals and the state of local transportation, which I do not know.