As the only remaining fully cast-iron church in the world, Istanbul's Bulgarian St. Stephen Church offers historians and those interested in religion an incredibly unique place to stop while on vacation.

This church on the shoreline of Istanbul looks ornate yet pretty normal – that is until you go up and take a closer look. The Bulgarian St. Stephen Church isn't made of stone but rather of cast iron. It's a rare survival of a 19th-century craze in prefab cast-iron churches.

Also known as the Bulgarian Iron Church, its parts were cast in Vienna in 1871 and shipped down the Danube in a hundred barges to be assembled in Istanbul. This building marks an important time in the Bulgarian Orthodox Church. Bulgaria and Greece were both ruled by the Ottoman Empire. Bulgarian Christians were under the domain of the Greek Patriarch, but the Bulgarians complained that he favored Greeks over Bulgarians.

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