Between San Sebastian and Barcelona at the end of June?

Hi, if using only trains, I think Zaragoza (note spelling) is your best (and probably only option). You see all west-east train travel from Basque Country to Catalonia runs through the Ebro River Valley where Zaragoza is the only rail hub in between.

Zaragoza is totally off the radar when it comes to foreign tourism, why RS and many Anglo-American guide books don't even think it exists lol! Zaragoza has more than 2,000 years of history including Roman ruins of the city walls, forum, and amphitheater, as well as the Aljafería; an 11th-century Moorish palace. It's also the home of the famous pilgrimage site of Nuestra Señora del Pilar Basilica, housing the Virgin Mary of Pilar. Excellent up and coming food and wine scene too.

If renting a car that gives you more options to go across the Pyrenees Mountains, visiting smaller villages and towns.

Everything Carlos said is true. We (two Australians - 59 and 72) spent three nights in Zaragoza in mid February and really, really enjoyed it. The Roman ruins were great, the basilica was great, the Aljafería was amazing. And we liked the food and the laid back lifestyle. It's on our "must go back to" list.

Zaragoza is an excellent option, but be aware that it can be blistering hot in the summer--not at all like San Sebastian. Be sure reviews of your chosen lodging don't include any quibbles about the air conditioning. The average high temperature at the end of June would be about 87 F. The record high is 106 F for June and 112 F for July.

Don't be tempted by a really attractive rate at the Eurostars hotel. It's at the train station, which is a nearly 20-minute walk from the Aljaferia Palace and perhaps double that from the historic center. There are buses, but they don't solve the problem of staying in a food desert in a hotel whose restaurant is closed in the summer (at least that was the case in 2016). To their credit, a few food items were available via room service. There was a cheese plate or fruit plate that was totally acceptable. The pizza was straight out of a frozen-pizza box.

If you're not up for the likely meteorological conditions of summertime Zaragoza, I wonder whether your Basque itinerary includes Bilbao and Hondarribia.

As always, great guidance from you experienced forum consultants! Muchas gracias!

I've been to Zaragoza a few times over the summer and have never had any heat issues. Last time I was there I stayed at Hotel NH Ciudad de Zaragoza, an incredible location for a very reasonable price, directly overlooking the Pilar Basilica and the old Roman walls, in the old town. Recently renovated and very tasteful.