Castle of Santiago de Fuentidueña Monument · Fuentidueña de Tajo, Las Vegas, Madrid Image of Fuentidueña de Tajo, not of the place itself. A 12th-century fortress remodelled in the 15th, also known as the Torre de los Piquillos, which belonged to the Order of Santiago and served as a prison for Don Álvaro de Luna; in ruins, it commands the Tagus crossing from the hilltop. Photo: esetena (CC BY 3.0) What to see and do in Fuentidueña de Tajo