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Hagia Sophia, the iconic Istanbul landmark described in detail by Evliya Çelebi, holds immense historical and architectural significance. Originally built as a basilica in the 6th century, it served as the Byzantine Empire's main cathedral and later as an Ottoman mosque. Today, it stands as a museum, showcasing its grand domed structure, awe-inspiring mosaics, and intricate marble work, symbolizing the fusion of diverse cultures and eras.