The Altamira Caves are located only 2km from Santillana del Mar and it's worth the trip to see the…read moreMuseum and the replication of the original cave (which is closed to the public). The Neocueva is a impressive reconstruction, the explanations are good, and the recreated and prone-painted bison-related art is enjoyable to look at and ponder prehistoric history. Gayle and I also enjoyed wandering through the attached Museum that puts this cave and many of the others in Europe into historical perspective. The paintings were first discovered in 1879 by Marcelino Sanz de Sautuola and was the first discovery of Paleolithic cave art. In 1973, 174,000 people visited the caves and it became evident that the visitor numbers was having a grave effect on the caves. A black mold started to cover the paintings caused by increased humidity due to the breath of visitors . In 1977 the caves were closed to the general public to protect the paintings. In 1982 it was decided to build an exact replica of the caves, this was opened in 2001. A small number of visitors are allowed to the original caves each year but the waiting list is very long. Gayle and I saw what we think was the old entrance as we walked along the spacious grounds. There's also a separate building that supports continuing research at this UNESCO Heritage Site.