Deservedly the most popular walk in the Picos takes hikers into the heart of the central massif, along the Cares Gorge (Desfiladero de Cares). Its most enclosed section, between Caín and Poncebos – a massive cleft more than 1000m deep and some 12km long – bores through awesome terrain along an amazing footpath hacked out of the cliff face. Maintained in excellent condition by the water authorities, it’s perfectly safe. Many day-trippers simply get a taste of it by walking as far as they choose to and from Caín, but with reasonable energy, it’s perfectly possible to hike its full length – in both directions – in well under a day.
The gorge proper begins immediately north of Caín. Just beyond the end of the road, the valley briefly opens out, but then, as you follow the river downstream, it suddenly disappears – a solid mountain wall blocks all but a thin vertical cleft. In its early stages, the trail burrows dramatically through the rock, before emerging onto a broad, well-constructed and well-maintained footpath, which owes its existence to a long-established hydroelectric scheme. During busy periods, the first few kilometres of the trail tend to be thronged with day-trippers thrilling at the dripping tunnels and walkways. Once you get 4km or so from Caín, however, the crowds thin out, and the mountains command your total attention. They rise pale and jagged on either side, with griffon vultures and other birds of prey circling the crags. The river drops steeply, some 150m below you at the first bridge, but closer to 300m by the end.
A little over halfway along, the canyon bends to the right and gradually widens along the descent to Poncebos. Roughly 7km and 9km into the gorge, enterprising individuals run makeshift, summer-only refreshments stands, handy as there are no springs. For its final 3km, the main route climbs a dry, exposed hillside; an alternative riverside path can be reached by a steep side-trail that zigzags down the precipice.
It is, of course, equally possible to walk all or part of the gorge from the north, starting at Poncebos.