This underground cistern was completed in 532 and used as a storage where the water was delivered to the city through the Valens Aquaduct. It has a size of 140mx70mx8m, with a total sum of 336 columns. The total water capacity is about 80,000m3, and openned to the public in 1987 afer the restoration.
The lighting and clasic music played brought in the mystic atmosphere in this underground palace.