Basilica Cistern
The large cistern provided a water source for the emperor's palace. Sometime before the Ottoman conquest of Constantinople in 1453 the cistern was closed. It was discovered in 1545 by Petrus Gyllius. After that Ottoman city officials used it for dumping waste including corpses. It has been restored at least three times. In 1985 it was closed for cleaning again. In 1987 it was opened to the public as a tourist attraction. 2 million tourists visited the Cistern in 2013.