Yaso, a small village belonging to the municipal council of Bierge, has just 11 inhabitants. It sits at a height of 692 metres on the southern slopes of the Arabgol range, within the Sierra de Guara Natural Park. It lies on the left bank of the Formiga River and is close to the road that joins Alburuela de Laliena with Aguas.

It is located on a slope at the foot of a peak known as Lacozán. The parish church dedicated to San Andrés welcomes visitors; it has a Romanesque building with nave covered by a barrel vault. The apse is semi-circular in shape and is covered by a semi-dome. The stone that can be seen reveals well-cut ashlars that are homogenous, broken only by the impost that runs around the church at the height of the vault’s springers and by the semi-circular window in the centre.

The church once boasted an interesting series of mural paintings in the lineal Gothic style that are currently on display in the Diocesan Museum of Huesca. Inside there is an 18th century baroque chapel with dramatic stuccoed decoration.

Along the village’s only street there are a number of interesting ancestral homes with heraldic coats of arms taking pride of place on the façade above the beautifully arched doorways.

The village dates back to the medieval era and was known as Eso during the 11th and 12th centuries; as Yeso from 1495 to 1609 and Jaso in 1785. In November of 1188, Alfonso II of Aragón awarded it to the Cistercian monastery of Casbas and it remained in their domain until the abolition of the nobility.