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. 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. In the time of the cave painters, the entrance to the cave was not as large as it is today, because it was enlarged by the excavations in the front of the caves.
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, completed with shadowing.