The Sierra de Guara is the southern edge of the Pyrenees, a rough range of sandstone and limestone where rivers have cut deep, dark canyons that are among the best in Europe for canyoning. The Abrigo de Arilla lies in that country, well off the main roads, in the lonely hills between Alquézar and the Sierra, and is one of the rock shelters of the Río Vero cultural park. The paintings are mostly Levantine and schematic, thousands of years old, and are part of the Mediterranean Basin rock art that UNESCO listed in 1998. Reaching the shelters generally requires a walk, and regulations apply.
Alquézar is the village to know in the area, a medieval hill town built around a collegiate church on a rocky spur above the Vero river, with arcaded streets and a long walkway along the canyon walls. It is deservedly popular, so go early or late. The region is also the home of the Somontano wine area, around Barbastro, whose reds and whites are good enough to deserve a place at lunch. In the Sierra the great bearded vulture, the lammergeier, nests on the cliffs and can sometimes be seen cruising the thermals with its wings held straight.
The riding is first class. Roads wind through the foothills with a series of long, flowing curves, climb in tight turns to viewpoints over the sierra, and plunge into gorges with sudden changes of light. Traffic is light outside August, and the surface is mostly good, though minor roads can be narrow and rough. The weather can change quickly in the mountains, and storms in summer can be violent, so check the sky in the afternoon.
Fuel is the thing to plan. Alquézar and the villages nearby have a few hundred people each, so fill up in Barbastro, which is a much larger town, before heading up into the hills. Bars in the villages serve coffee and good sandwiches, and in Alquézar a dinner of local lamb with Somontano wine is worth the effort. Spring and autumn are the best seasons, with clear air and warm days, while the high roads are cold in winter.