In addition to
@wisepilgrim , you cannot walk 3 weeks from Porto to Redondela where the coastal ends in an estuary unless your pace is as slow as a snail or you go two steps ahead and one beyond
It is about 110 kms in Portugal and about 70 kms in Galicia along the coast.
Except for the mountain in A Guarda there is only a flat walk all the way but leaving Baiona and arriving at the bridge in Nivran , do not follow the yellow waymarkers but directly after the bridge follow green waymarkers and you stay at the coastline to Vigo and even arrive there at sealevel .
The yellow waymarkers lead you into the highest part in Vigo but you will descent in town to sealevel to follow the estuary to Redondela
You even can walk some kms on the beach as you also can do between Matosinhos and almost to Vila do Conde if you want to.