The Basilica Cistern in istanbul

Basilica Cistern is another popular attraction located near Sultan Ahmed Mosque (Blue Mosque) and Hagia Sophia. It is quite unique and in my opinion well worth a visit.

It is even more spectacular if you look at it through the prism of time. It was built in the 6th century AD during the reign of Byzantine Emperor Justinian I and is the largest of several hundred ancient cisterns that lie beneath the city of Istanbul. It must have been quite an architectural challenge and it is no wonder that 7,000 slaves were involved in its construction.
Hundreds of them died during the process. This might be the reason for an eye with tears engraving on one of the columns.

It is basically a huge underground chamber approximately 140 metres (450 ft) by 65 metres (210 ft) and is capable of holding 80,000 cubic metres (2,800,000 cu ft) or 100,000 tons of water. The ceiling is supported by 336, nine metre (30 ft) high, marble columns (mostly carved in Ionic and Corinthian styles).

Its initial purpose was to store and filter water for the Great Palace of Constantinople and other buildings on the First Hill. It continued to provide water to the Topkapi Palace even after the Ottoman conquest and also into the modern times.

At the far end (northwest corner) of the cistern there is a couple of Medusa column bases. One is placed sideways and the other upside down. According to tradition the blocks are oriented sideways and inverted in order to negate the power of the Medusa's gaze.

The place is lit with water reflections in mind and the effect is aimed to emphasize the countless number of columns. I hope this is obvious from the included photos.
There are even some fish traces visible on the first photo.

At the time of our visit the entrance fee was 10 TL. Basilica Cistern is open every day from 09:00 until 18:30. It took us almost an hour to walk through the place and take those countless photos. I guess without a camera it could be done much quicker.