For centuries, Els Vilars (or Vilasos), a small cave to the West of Os de Balaguer, was used as a shelter by shepherds, evidence of which can be seen on the walls and blackened ceilings. However, it was not until the 1970s that 4,000-year-old old cave paintings were discovered behind the smoke marks. Currently they form part of the collection of Rock Art of the Mediterranean Basin on the Iberian Peninsula, which was declared a World Heritage Site in 1998.

Despite its small size -no more than 60 m2- the cave is richly decorated: up to 28 figures or tracings have been identified. Altogether there are three groups of figures that are particularly significant due to their content. The first consists of a dance scene, in which a man has his arms around the waists of two women dressed in skirts that are typical in Levantine cave painting. The three figures are painted in a deep red.

Another of the groups comprises four concentric circles and is believed to be a heliolithic representation, a tribute to the Sun. Finally, at the back of the cave, there is a hunting scene, where goats, wolves, foxes, and even a doe are all depicted.

The location of the cave is excellent.Thanks to its position, it receives the first ray of sunlight and, at the same time, it provides a wide view of the Valley of the River Farfanya.