Basilica Cistern in Istanbul is the largest of several hundred ancient cisterns that one can find under the city of Istanbul. The cistern was built in the 6th century during the reign of Byzantine Emperor Justinian I. Basilica Cistern is carved at more than 150 m beneath the level of the street and his job is to store pure waters.(now you can see some fishes also in the water).
The strangest is the pic. nr. 2: a pillar with a Medusa head put upside down. 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.
The view at 150 m underground seems not real. The lights that underline the slim columns are amazing: I had the impression that the chamber was even higher, like double sized. The air is pure, one can hear only the fishes splashing the glittering surface of the water. In total, 80.000 cube meters of stored water that once could provide water for the Great palace of Constantinopole and other buildings on the First Hill and Topkapi palace.