Castillo de Castronuevo stands as an exceptionally well-preserved fortification erected by Gil de Vivero before 1481 near Rivilla de Barajas in Ávila province, reflecting the instability of Henry IV's succession period. The fortress features five towers—three circular and two rectangular in floor plan—surrounded by a defensive barrier incorporating an artillery parapet and moat, with loopholes strategically placed for optimal defense and Gothic-Mudéjar architectural elements visible throughout its design. Its most remarkable feature comprises some of Europe's best-preserved underground vaults constructed from brick, originally serving as stables and demonstrating sophisticated medieval engineering. After Vivero's son remodeled the structure, it was sold to the Duke of Alba in 1489 and remains property of the House of Alba today, accessible only from the exterior as a private fortification that exemplifies 15th-century castle design and construction techniques.
