The Palacio Ducal de Medina Sidonia is one of Spain's most remarkable private archives — a ducal palace still run by the Guzmán family (now the Duchess of Medina Sidonia Foundation) that contains over 800 years of documents relating to Spanish colonial history, the Armada, and the politics of the Andalucían nobility. The archive is open to researchers by appointment, but the palace itself offers guided tours.
The rooms are stacked with portraits, arms, ceramics, and furniture accumulated over generations by one of the most powerful families in Spanish history. The Duke of Medina Sidonia commanded the Spanish Armada in 1588 — reluctantly, by his own account — and the palace still has documents from that period. The building itself, with its long whitewashed façade in the heart of the upper town, is architecturally modest by ducal standards, which makes the richness of what's inside all the more surprising.