The Basilica Cistern, also known as the Yerebatan Cistern, is a subterranean water storage system located in the heart of Istanbul, Turkey. Built in the 6th century during the reign of Byzantine Emperor Justinian I, the cistern was used to provide water to the Great Palace and surrounding buildings.

The cistern measures 140 meters by 70 meters, with a capacity of up to 80,000 cubic meters of water. The cistern features 336 columns, many of which were salvaged from earlier structures, including the Temple of Artemis in Ephesus.

Today, visitors can explore the cistern and marvel at the columns and architecture. The cistern has been featured in several films and books, including Dan Brown’s novel “Inferno.” One of the most striking features of the cistern is the two Medusa heads, which are believed to have been brought from a nearby pagan temple and placed upside down in the cistern to ward off evil spirits.

Overall, the Basilica Cistern is a must-visit attraction for anyone interested in Istanbul’s rich history and architecture.