Castillo de Castañares de las Cuevas is a unique medieval fortress carved into the natural caverns of a ravine in the Sierra de Moncalvillo near Viguera, La Rioja. Built into two sections of three stories each, the castle ingeniously adapted its irregular design to the existing rock formations and cave systems, featuring a 22-meter cave with a natural spring and a 13-meter connecting corridor. Dating to the 12th and 14th centuries, the structure was reconstructed during the lordship of Iñigo Ortiz de Zúñiga of the prominent Zúñiga family, with possible earlier use dating to the 10th century. This fortress represents an exceptional example of medieval engineering that maximized natural defensive advantages through its integration with the mountainous terrain.
