Osma Castle is situated next to the town of El Burgo de Osma, in the western part of the province of Soria in Spain.
On a hill between the rivers Ucero and Avion, close to the ancient Roman city of Uxama and dominating the today humble, but formerly important, town of Osma, lie the remains of this once strong castle. It once possessed three walled enclosures of which nowadays some remains can be seen. The highest inner enclosure makes up the present castle with remains of a keep and other buildings. Along the outline of the lowest and largest outer enclosure, running down the slope of the hill, next to the riverbank, stands a ruined tower called; Torre del Aqua (Tower of the Water). It is constructed, as are some parts of the castle, with building materials taken from the ruins of nearby Uxama.
The medieval Osma Castle, built in 912 and conquered for the first time by King Garcia of Leon, underwent innumerable sieges and devastations due to Moorish expeditions that took place during the 10th and 11th century. Until 1088 when it was taken by king Alfonso VI during the Reconquest.
The town of Osma was founded in the 12th century along with its primitive Roman Catholic cathedral de San Pedro de Osma. As the town became more important than the castle it was equipped with great city walls, which are partially conserved today, in the 15th century by the bishop Pedro de Montoya, who also fortified nearby Ucero Castle.
Osma Castle is a nice ruin and can be visited freely. There isn't much to be seen inside but its a nice walk up the hill and the views from above are great.