Cuevas de Castañar Nature · Castañar de Ibor, Villuercas-Ibores-Jara, Cáceres Image of Castañar de Ibor, not of the place itself. Discovered in 1967 and declared a Natural Monument in 1997, they feature fine aragonite speleothems and preserve 540-million-year-old fossils of Cloudina carinata, among the oldest invertebrate remains in Europe. declaradas Monumento Natural en 1997 Photo: Luis Rogelio HM (CC BY-SA 2.0) What to see and do in Castañar de Ibor