I went to the northern coast of Spain with my family two weeks ago. There you can find both beaches and mountains. Although the weather is usually rainy and cloudy, we had a splendid week. It was sunny everyday and we could spent our time together having a bath on the sea or visiting the beautiful villages of Cantabria.

We stayed in a camping where the staff was so kindly and it had lots of services. The children enjoyed visiting every beach of the coast and, although the water was so cold, they got amazed with the waves. 

I recommend strongly the visit of the North of Spain. It will surprise you and there is not as many people as in the Mediterranean coast.