1-3 Locations for N. Spain/Basque Day Tripping

We chose to stay in Hondarribia for a week as a base and enjoyed this town and the ease of driving to other Basque towns. Do not miss the French Basque villages across the border either with their pelota courts and red trimmed houses. Ascain, Ainhoa, Saré, Espellette are a few we enjoyed.
We explored many Spanish Basque towns Lekeitio, Getxo, Guernica, Getaria.
It was very helpful to have read Mark Kurlansky’s “ The Basque History of the World” before our trip.

Well I guess it depends how far west you plan to travel? To Santiago de Compostela? Northern Spain encompasses a vast sway of territory, the Basque country accounts for only 1/5th of what the north offers. If wanting to stay more central/east wards as you will finish in Barcelona, I can recommend these smaller scenic towns:

Potes - charming alpine town, the perfect base for exploring the Picos de Europa National Park

Tarazona - medieval town where Muslims, Christians and Jews all lived in harmony. The town's unique architectural eye candy reflects this synergy between the three cultures. Tarazona’s medieval Jewish Quarter is the best preserved in the region. Good base to explore underrated Aragon/Navarra regions.

I've only been to the bigger towns in the Basque Country.

PS: April is the height of the rainy season in northern Spain, be prepared.

Three weeks is a long stretch of time, so I would plan a trip from east to west or the other way around (500miles from one end to the other). You can start in Galicia, with Santiago de Compostela as a base for around 4 days in the Galicia region, heading east towards probably Lastres, Cudillero, Potes inland...for another 4 or 5 days in Asturias; then further east with maybe Comillas or neighboring towns as the home base for Cantabria, and then maybe Getxo, Plentzia, Elorrio inland, Zumaia, Getaria...as a good base in the Basque Country. If bigger towns, Gijón or Oviedo, Santander, Bilbao and Donostia-San Sebastian make good departing points to explore the north.

I highly recommend you follow poster Mike above. His suggestions are perfect. We entered Spain from Porto, Portugal and followed many of the routes he suggests.

We visited northern Spain a few years ago and rather than taking day trips, we changed locations every two or three days. For us, a week is too long in the same place. The order of our trip by the locations we stayed was, Zamora, León, Villafranca de Bierzo, Santiago de Compostela, Ribadeo, Santillana Del Mar, Hondarrbia, Bayonne, Pamplona, Santo Domingo de La Calzada, Burgos, Tordesillas, then back to Madrid.

Between lodging locations we stopped at other places, such as, Arévalo, Valencia de Don Juan, Astorga, Muxia, As Catedrais beach, Cangas de Onis, Sanctuary of Covadonga, Zumaia, Gertaria, and Saint-Jean-Pied-de-Port.

If you decided to visit Tarazona, you may want to stop at Trasmoz (town excommunicated by the Pope centuries ago for witchcraft) and Ágreda (to see the Blue Nun). There are numerous places in the Logroño area worth visiting, like Estella, Puente de la Reina, Monastery of Iranzu, Olite, Artajona, and the list could go on.

Thank you, everyone, for your wonderful help. Suki, I ordered the book and will read it! I took Carlos' advice about weather seriously and we decided to revise our travel schedule to begin in Barcelona with granddaughter. Then, we'll head west from there to the central, Basque (Spain & France), west coast (perhaps Santiago del Compostela) and loop back into Madrid to perhaps revisit before flying out. Perhaps we'll need to spend less than a week in a location given all the hopping and skipping, which is normally not modus operandi for us. We tend to prefer having a kitchen as we have food issues and don't adjust very well to the late dining hour in Spain. I'm sure I'll be back with more questions. Muchas gracias y eskerrik asko!