Recommend a beach location in the Basque Country, city?
San Sebastián - Bilbao - Castro Urdiales - Laredo - Santander and beyond. If you are driving - you can just go along the coast, it's beautiful everywhere here. There are small cozy towns like Bermeo, and there are larger ones. High cliffs, beautiful bays. In July, it's already quite swimmable.
You need to be prepared that it is not hot in the north, it will be a maximum of 20-25 degrees, and the water will be around 20-22 degrees. But it is very green and beautiful!