This is relatively high alpine—there will likely be snow fields to cross, even in summer. Be sure if you are attempting in any season other than summer to do your research and have the proper equipment.
This run begins near the town of Sotres in Los Picos de Europa National Park. From the main park road, continue slightly right downhill at the fork (left leads up to the town of Sotres) which will lead you through a small abandoned village (Aldea de Los Invernales de Texu). Follow this road through the village, up the hillside, until it eventually comes to an end (approx. 4.2km from the fork in the road).
The trail is well maintained and easy to follow. It passes by more abandoned stone houses, villages, refugios, etc. The views are stunning with high mountain peaks, rivers, villages in the distance, etc. You'll probably encounter cows and goats along the way.