Spain and France

Hi!
Segovia could be a hub for 2-3 nights including day trips to Ávila (more like 1/2 a day) and Pedraza.
León is too far west, I would skip it and replace with Burgos. Whether you need an overnight stay in Burgos is debatable - a relatively nearby option (1 hour further) would be the charming Rioja village of Laguardia, or you could press on towards the Basque Country.
There is a lot to explore between Bilbao and San Sebastián, so you will have to make a few choices.
Also, rather than Bordeaux, I would explore the French side of the Basque country for those 2 days. Car not needed if you stick to the coast.
I would then take the train north to Caen via Tours and rent a car there for Normandy, then Mont Saint Michel, then drop the car off in Rennes to head to Paris.

Now, this is a lot of travel for the time you have. Is there any way you could extend the trip? Another 3-4 nights sprinkled throughout would make the pace more bearable.

Thank you for the reply. We arrive on April 14 and fly home on the 7th of may

Semana Santa will be in full swing when you arrive, its a very big deal in Spain, think of it like Christmas week, for example Easter Monday, April 18 is a national holiday with many shops and restaurants being closed. Many locals will take advantage of the long holiday weekend to travel domestically so you may find some logistical issues/price increases with hotels in the popular tourist areas.

That being said, since you mention an interest in smaller towns, I'd suggest you swing east wards through southernwest part of the Aragon region before making your way up to San Sebastian. For example you could base yourselves in Tarazona, which I'd describe as a "mini Toledo", as this small town has a long history during which 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.

From Tarazona one can make several daytrips, to the Calatayud wine region, Olite royal palace, or witches' village of Trasmoz.

PS: Be prepared for lots of rain in April, especially the more north you go. In Spain we have a saying "en Abril aguas mil" which means "in April a thousand waters".

There are a lot of good suggestions here. I'd like to reinforce the comment about Avila--in fact I will go farther: Avila has a walkable wall and not much else of interest. Segovia, Tarazona, Burgos, Olite and Laguardia are places I liked a lot more. I will warn you that Olite (despite its interesting castle) is rather lightly visited. Do not arrive in town hungry at off hours lest you find nowhere to eat. Laguardia is a medieval hill town. Research parking ahead of time. You'll be parking the car below the town, but there's at least one elevator up; best to know where that is in comparison to your parking options.

In addition to the Guggenheim, Bilbao has a large historic area, the Casco Viejo. It's much larger than what you'll find in San Sebastian and much, much less touristy. Between San Sebastian and the French border is the town of Hondarribia. It has a very atmospheric historic district on top of the hill and some seafood restaurants down at water level.

In the French Basque Country I preferred Bayonne as an overnight stop because of its relatively large historic area. St-Jean-de-Luz is a cute coastal town. I didn't like Biarritz as much, but I hit a really rainy day, which probably affected my attitude.

Bordeaux is an attractive city but feels rather large. Since you're not into museums, you might prefer to stop in a smaller place. From the train standpoint, though, Bordeaux definitely has an advantage.