There's much to see without driving far today, starting at the Santimamiñe caves. 

Part of the UNESCO World Heritage site which covers the Paleolithic cave art of northern Spain, these caves are the most significant ancient paintings in the Basque Country. Although access is heavily restricted, there is a first-rate virtual headset experience here which, combined with your being able to peek inside the real caves, makes for a fascinating visit.

Tucked away in the forests of the hill opposite is the marvellous 'Painted Forest'. After a pleasant walk of a couple of kilometres, you walk into a section of forest in which 34 different works of Land Art have been created by local artist Agustín Ibarrola. The clusters of trees reveal themes and collages which are best seen from specific viewpoints marked on the forest floor. It's a rather magical place and a splendid place for a picnic. 

With your head full of art and belly full of food, you might like to break your journey home with a walk up to a hilltop chapel for views out along the coast and down the estuary. Alternatively, stop at the beach for a cup of tea, or cold beer and perhaps a splash in the waves before you return to your hotel.