If you can only do one walk when visiting de Picos, this might be an excellent choice. It is a very popular walk through the valley of the Cares river. You can start the walk either from the North side (seaside) from Poncebos, which is I believe the more popular starting point, or from the South side from Cain or Posada de Valdeon. From Poncebos you starts with a steep uphill walk for about 2 km. The walk takes about 3 hours to reach Cain. The roundtrip Poncebos-Cain-Poncebos will be a total distance of 24 km. Or you can start from the other side from Posada de Valdeon or from Cain. The walk from Posada de Valdeon to Cain takes 2 hours and 15 minutes. If you start from Cain, you immediately start with the most spectacular part of the walk. But then you have to drive up to Cain first of course. In summer there are busses going up to Posada de Valdeon.
We drove from Potes and it took us a bit under two hours to reach Cain. The road goes through beautiful mountain landscape. On the last part between Posada de Valdeon and Cain, the road becomes very narrow and on most places only one car can pass at a time. We were lucky and did not have any oncoming cars. There are a few small parking areas in Cain, but I can imagine that in July or August it might be difficult to park you car if you do not come in time.
Cain has several small restaurants. We decided to have a bite before our walk since it was already 1 PM. We chose Albuergue El Diablo de la Peña, where we shared a salad. This is a really nice restaurant and hostel.
We then started our walk. Just walk de road down through the village and you automatically come onto the Ruta del Cares (the Caress route). You have to cross a bridge over the Cares river.
A bit further there is a dam at the entrance of the gorge know as the Golden Gorge (Garganta Divina), because of its spectacular beauty. The road here is hacked out of the mountain. This trail was originally made for the maintanance of the Dobresengos water canal between Cain and Poncebos that was built between 1915 and 1921. The canal still functions, and you will see the canal a bit further next to the road. The walk is quite flat.
You cross the gorge three or four times by a bridge. The views of the gorge with the river down below are spectacular. At one point you come onto a wooden passerelle ( Martinez Passage) that hangs over the gorge. It was constructed to remplace a part of a tunnel that had collapsed. You often also meet goats along the way.
We walked half of the route (1,5 hour) and then turend back to Cain, so we walked about 3 hours, but made many stops to take pictures and enjoy the landscape. So we probably spend about 4,5 hours. The route is breathtaking, and is highly recommended. I would not take small kids though. The road is quite narrow in some places and on the side of the gorge there is no barrier. We did meet a dad with two children of whom the youngest was no more then 9 I think, but they were very well behaved, and listened well to their dad. And they looked as if they were used to mountaineering.
In Cain we took an early dinner in the same restaurant; Albuergue El Diablo de la Peña. We tried the local Asturian specialties; Fabada: a stew of large white beans with meat (morcilla, pork shoulder and chorizo) and saffron and Morcilla: a kind of blood sausage pudding of local pork with Valdeon cheese (blue cheese from Leon). Very special and very tasty dishes, typical mountainous food.