The Yuso and Suso Monasteries are in the village of San Millán de la Cogolla and are European Heritage Sites.
Suso, the upper of the two monasteries began in the caves inhabited by the hermits and disciples of San Millán in around the 6th century. The building work that turned these caves into the monastery is reflected in the different architectural styles layered on top of each other from the 6th to the 10th centuries: Visigoth, Mozarabic and Romanesque. Suso's cultural importance comes from the collection of manuscripts and texts written at the Monastery's library make this one of the most important, if not the most important, libraries during Spain's Middle Ages. This setting provided the backdrop for what is today the oldest written evidence of the Spanish language.
The Yuso Monastery was built to expand the Suso Monastery in the 11th century and is particularly large. It was built during the 16th, 17th and 18th centuries and combines different architectural styles: mainly Renaissance and Baroque. The Monastery's museum houses many wonderful works of art.