The fortified monastery dominating the hilltop of Hora is one of the great monuments of Eastern Orthodox Christianity. Founded in 1088, its thick defensive walls give it the appearance of a medieval castle from the outside — from the sea approach, it dominates the island's skyline completely. Inside, the complex spreads across several levels of courtyards, chapels, and galleries, built and expanded over ten centuries.
The treasury museum is the highlight: it holds 33 pages of the Codex Porphyrius, an early 6th-century purple parchment Gospel, along with chrysobulls from Byzantine emperors, jewelled vestments, and an extraordinary collection of illuminated manuscripts. Dress modestly (no bare shoulders or shorts), arrive early in summer before the cruise day-trippers arrive, and allow at least two hours.