Because next to the Topkapi are two of the most breathtaking structures of the world. There is the Hagia Sophia Museum &mdash or the Aya Sofya Museum, depending on your favoured selection of history (after a while, one gets used to several names &mdash Greek, Roman, Persian, Turk &mdash for the same site in Turkey). Although secularised in 1935, the scale of the edifice very nearly makes one believe in a power supernatural. There is still public pressure to open it for prayers, but the government has held on to the law that made a museum out of a mosque which was earlier the world&rsquos largest cathedral for a thousand years. It sits under the world&rsquos most famous dome, more a tribute to Byzantine engineering than any one religion. Not far from it is one of the grandest buildings it inspired, the Blue Mosque with its six minars.