Some of the oldest paintings in Europe sit in a hill above a village best known for its hot springs. The cave of El Castillo opens in the flank of Monte Castillo, right above Puente Viesgo in the Pas valley of Cantabria, and inside it are hand stencils and a red disc that scientists dated, in 2012, to more than forty thousand years ago. That makes them contenders for the oldest cave art known on the continent, and possibly older than any made by modern humans, since Neanderthals were around at the time. UNESCO lists the Cantabrian caves, and a visit means a guided group entering in small numbers, so book ahead and expect limits on the day.
The Pas valley is green all year, and the roads show it. From Torrelavega the main road climbs gently through meadows, eucalyptus plantations and stone villages, with the river beside you and mist hanging on the slopes. Beyond Puente Viesgo the road continues toward the Pas passes, where the bends tighten and the views open onto steep grassy ridges dotted with cattle. Rain is frequent here, so a waterproof is not optional, and in wet conditions the surface can be greasy under the trees. The best riding is in late spring and early autumn, when the air is fresh and the mountains clear.
Puente Viesgo has about two and a half thousand people and a long history as a spa, with warm mineral water that has drawn visitors since the nineteenth century. There is a petrol station within reach and a handful of places to eat, and Torrelavega, nine kilometres away, offers everything else. Try the local dairy, such as quesada or sobaos pasiegos, light sponge cakes baked in the valley.
Monte Castillo has several caves, and they differ in what they offer, so ask at the visitor centre which are open. After your visit, walk down to the river and listen. The place feels private and strangely patient, as if the mountain had been keeping its secret long enough to forget it was one.