Some 14km south of El Burgo de Osma, one of Spain's most remarkable castles rises above the virtual ghost town of Gormaz (population 21). Built by the Muslims in the 10th century and reportedly the largest Muslim fortress in Europe, the castle was for centuries an important bastion along the frontier between Islamic armies and the Christian forces of the Reconquista. Most of its 21 towers remain and the walls stretch for over a kilometre.
The castle is reached via a winding road about 2km beyond the modern village. From the end of the road, climb up through the main gate and wander at will around the ramparts, which still convey enormous dignity – the views alone justify the effort of getting here. At the eastern end, behind the Torre del Homenaje, is the Alcázar, where the military governor lived and which represented the castle's last line of defence; note the deep wells that enabled the castle to withstand a siege.
The castle remained in Muslim hands for more than 60 years after it was built before it fell to Fernando I in 1059. It remained a military fortification until the 15th century, when it was converted into a military prison.