El Cabezo de Castildetierra y las Bardenas Reales Nature · Arguedas, Ribera, Navarra Image of Arguedas, not of the place itself. The Bardenas Reales are a semi-desert area of 41,845 hectares of clay, gypsum and sandstone eroded by water and wind, managed since 1705 by a community of 22 co-owning entities (19 municipalities, 2 valleys and a monastery) with historic grazing rights. On 6 April 1999 they were declared a nature reserve, and on 7 November 2000 UNESCO recognized them as a Biosphere Reserve, the first in Navarre. Its most photographed icon, the Cabezo de Castildetierra, is a 'fairy chimney' formation — a layer of more resistant rock over soft material — located within the boundaries of Arguedas, next to the park's visitor center at the Finca de los Aguilares. 2000 Photo: Jialxv (CC BY-SA 4.0) What to see and do in Arguedas