The Basilica Cistern is the largest of several hundred cisterns that lie beneath the city of Istanbul.
This massive underground chamber was built during the reign of Byzantine Emperor Justinian I in the 6th Century. It was used to collect and store water for the Great Palace and other nearby buildings.
The cistern covers an impressive 2.4 acres and can hold over 21 million gallons of water.
Today, visitors can spend up to an hour exploring the beautiful underworld while enjoying atmospheric lighting and soft music.