The PR-HU 89 Castejón de Sos – Arasán trail is one of the most interesting routes in the Ésera Valley, combining natural landscapes, charming villages, and a significant historical heritage. The route connects Castejón de Sos, Bisaurri, Urmella, and Arasán , and can be combined with the PR-HU 88 trail for a circular return.

The hike begins in Castejón de Sos , from where you cross the bridge over the Urmella ravine. From there, you follow a track that climbs gently through the woods until you reach Bisaurri , a village that retains much of its traditional character.

From this point, the path becomes a bridleway , sheltered by a lush canopy of ash, oak, and hazel trees. The route crosses the Riato ravine via a wooden footbridge and ascends to the hamlet of Urmella , divided into two neighborhoods. In the upper neighborhood stands the Monastery of Saints Justus and Pastor , one of the oldest in Aragon, founded in the 11th century in the Lombard Romanesque style, when Ribagorza was still an independent county.

The route continues towards Arasán , whose town center is notable for its well-preserved traditional architecture. This is an ideal place to stop and enjoy the surroundings before deciding to return.

There are two options to return to Castejón de Sos : do it by the same way you came or connect with the PR-HU 88 , thus completing a circular route.