Castillo de Lanos, also known as Castillo de Ocio, perches on an elevated cliff overlooking the small village of Ocio in Zambrana's Inglares river valley. This 12th-century fortress guarded one of Navarra's strategic borders with Castile, controlling two critical medieval routes: one linking the Inglares valley to the Ebro corridor, and another connecting the Ebro valley to La Rioja through the Lobera pass. Ingeniously built from sandstone and extremely durable mortar that resembles solid rock, the castle's rectangular keep and attached residential quarters are defended by natural cliffs on three sides, making it nearly impregnable. Today the ruins stand as a dramatic testament to medieval military engineering in a remote Basque Country setting.