Stunning underground cistern draws tens of thousands of tourists a day in Istanbul

It may look like an ancient palace or place of worship, but this stunning structure had a more mundane function: storing water.

Situated 20 meters (65 ft.) below ground, the cavernous and structure is a relic of past civilizations.

Known as the Basilica Cistern, it was built during the Byzantine Empire and reached its present state under Emperor Justinian who reconstructed it in the 6th century.

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