Basilica Cistern

The Basilica Cistern, known in Turkish as Yerebatan Sarnıcı, is the largest of the ancient underground water reservoirs beneath Istanbul. It was built in the sixth century during the reign of the Byzantine emperor Justinian I, close to the Hagia Sophia, to store water carried by aqueduct to the great palace and surrounding buildings. The vast subterranean hall is supported by 336 marble columns arranged in rows, many reused from earlier structures, and at its far corners two column bases rest on carved Medusa heads, one inverted and one on its side, whose original purpose is uncertain.

The dim light, dripping water and the enigmatic Medusa heads have given the cistern a reputation for the mysterious, and it features in fiction and film as an atmospheric, otherworldly place. Reports of an uncanny mood are subjective impressions produced by the setting rather than accounts of anything supernatural.

As a masterpiece of Byzantine engineering and one of Istanbul's most evocative monuments, the Basilica Cistern is of high historical value. After extensive restoration it reopened with new lighting and walkways, and it remains among the most visited sites in the historic Sultanahmet district.

The Basilica Cistern operates as a museum under the Istanbul Metropolitan Municipality's cultural body and is open to visit every day, including evening "night" sessions, via raised walkways over the water. Official information is provided on the venue's website.

Admission is ticketed, with day and night pricing, and official tickets are sold on site and through the authorised online partner; visitors are cautioned against similarly named reseller sites. The interior is cool, damp and dimly lit with some steps, so careful footing is advised.