For 6 weeks, I walked from Bidart France, to Finisterra on the very western coast of Spain. The route I took brought me along Spain's northern coastline. I had the sea on one side, and the mountains on the other. The walk was around 1000+km. Currently I'm working my way through the images from the trip, and I hope to make a book.
For the time being, here's an article with travelling advice from the 1400's.