Donostia, also known as San Sebastián is a very, very special city in NE Spain. A stunning city with amazing scenery, beaches, cycle paths, food, cliffs, walks ..... It is up there with the very best Europe can offer
Logrono is a couple of hours South and a small city/ large town and capital of the Rioja wine district and worth a trip too. Good informal night life/ tapas/ booze-up
Spanish supermarkets are virtually invisible. My guess is that Planners deliberately hide them. So if you see one, load up on your essentials.
Bay of biscay can be rough so consider sea sickness tablets. Food and booze on the ferry quite pricey, so you could take it from your Cali on arrival and eat your own stuff to save some cash.
Aa website will tell you about additional Spanish road regulations.