Cave of El Castillo
The Cueva de El Castillo, or the Cave of the Castle, is an archaeological site within the complex of the Caves of Monte Castillo, and is located in Puente Viesgo, in the province of Cantabria, Spain. It contains the oldest known cave art in the world. Hand stencils and disks made by blowing paint onto the wall in El Castillo cave were found to date back to at least 40,800 years, making them the oldest known cave art in Europe, 5-10,000 years older than previous examples from France. 
As traditional methods such as radiocarbon dating do not work where there is no organic pigment, a team of UK, Spanish and Portuguese researchers led by Dr. Alistair Pike of the University of Bristol, UK dated the formation of tiny stalactites on top of the paintings using the radioactive decay of uranium. This gave a minimum age for the art. Where larger stalagmites had been painted, maximum ages were also obtained.
This cave was discovered in 1903 by Hermilio Alcalde del Río, the Spanish archaeologist, who was one of the pioneers in the study of the earliest cave paintings of Cantabria. The entrance to the cave was smaller in the past, but it has been enlarged as a result of archeological excavations.
By way of this entrance one can access the different rooms in which Alcalde del Río found an extensive sequence of images. The paintings and other markings span from the Lower Paleolithic to the Bronze Age, and even into the Middle Ages. There are over 150 figures already catalogued, including those that emphasize the engravings of a few deer, complete with shadowing.
- Clottes, Jean (2003). Chauvet Cave: The Art of Earliest Times. Paul G. Bahn (translator). University of Utah Press. ISBN 0-87480-758-1. Translation of La Grotte Chauvet, l'art des origins, Éditions du Seuil, 2001, p. 214.
- Amos, Jonathan (June 14, 2012). "Red dot becomes 'oldest cave art'". BBC News. Archived from the original on 2012-06-15. Retrieved 15 June 2012. "One motif – a faint red dot – is said to be more than 40,000 years old."
- Pike, A. W. G.; Hoffmann, D. L.; Garcia-Diez, M.; Pettitt, P. B.; Alcolea, J.; De Balbin, R.; Gonzalez-Sainz, C.; de las Heras, C.; Lasheras, J. A.; Montes, R.; Zilhao, J. (14 June 2012). "U-Series Dating of Paleolithic Art in 11 Caves in Spain". Science 336 (6087): 1409–1413. doi:10.1126/science.1219957.
- Caves of Cantabria - Spanish Government Council of Culture, Tourism and Sport
- Video: Paleolithic Cave Arts in Northern Spain: El Castillo Cave