Ribeira de Piscos is a small stream that runs into the Côa, and its banks hold some of the best rock art in the valley. The engravings are cut into smooth, vertical slabs of schist, and they show what the hunters here cared about: aurochs with long curving horns, wild horses, ibex and deer, drawn in fine lines that overlap in layers, as if each generation added to the work of the one before. Some are about twenty thousand years old, and some were made later, in the Iron Age. The panels can be seen only on a guided visit, usually by four-wheel-drive vehicle from the museum in Foz Côa, so booking ahead is sensible.
The guide matters. In the harsh light of midday the engravings are almost invisible, but when the sun is low and slanting, or when the guide wets the rock, the lines leap into view, a bull's back, a horse's neck, a head turned. It is a strange sensation to see them emerge, as if the animals were stepping out of the stone, and it is the sort of experience that quietens a group.
Quinta dos Poios belongs to the other side of the valley's character. A quinta is a wine estate, and in the Douro region many of them sit on the terraced slopes, with vines in neat rows above the river, an old house at the bottom and a winery in the shed behind. The Alto Douro Wine Region, listed by UNESCO in 2001, is one of the oldest demarcated vineyards in the world, and the combination of ancient art and old vines makes the district unusual.
Riding here is a matter of small, steep roads and dirt tracks. The tarmac is generally decent on the main routes, but the lanes down to the river can be rough, with loose stone and sudden bends, and you may need to leave the bike at the top and continue on foot or by jeep. Summers are very hot, with temperatures above forty degrees, and the shade is thin. Spring brings wildflowers and almond blossom, and autumn brings the harvest.
Fuel is available at Vila Nova de Foz Côa, about seven kilometres away, which has stations, cafes and shops, and Mêda, farther away, has a smaller supply. Fill up in town, and carry water and sun protection.
Start in the morning, and keep an eye on the light. The best engravings are the ones you nearly miss.