I went to this place.. called Yerebatan Sarnici also called the Bascilica Sistern. This is the largest of several hundred ancient cisterns that lie beneath the city of Istanbul formerly Constantinople.
It was all under the ground and had one of the most amazing feelings. Cold. Dark. Nicely Lit. There were loads of fish swimming in the water.
In the corner of the cistern, there are two columns with the face of Medusa at the base. The origin of the two heads is unknown, though it is thought that the heads were brought to the cistern after being removed from a building of the late Roman period. Tradition has it that the blocks are tipped sideways and upside down in order to scare off the power of the Gorgons' gaze.
It is one of the sweetest things I have ever seen..