The Underground Cistern is one of the most extraordinary and impressive buildings in Istanbul. It is open every day from 9 am to 5 pm. The admission costs 10 YTL. (8 USD or 7 EUR) in 2006 season. he structure was known in Byzantium as "Basilica Cistern" because it lay beneath the Stoa Basilica, the great public square on the First Hill. The Basilica Cistern was built by Justinian I after the bloody NikaRevolt in 532, probably as an enlargement of an earlier cistern which it was constructed by Constantine the Great. During the Byzantium Period, it was used as a reservoir for water storage for the Great Palace and other buildings in the First Hill. During the Ottoman Period, the water was used for Topkapi Palace and watering theThe head of Medusa gardens of it. However the cistern had its brighest days during the Byzantium Period.The interior of Underground Cistern is breathtaking. It is 138 m, 452 ft long by 65m, 213 ft wide. There are 336 columns in the cistern. Most of the column capitals are either in Corinthian or Doric Style. At the far end of the Cistern, there are two heads of Medusa which are put upside down or side ways. The Medusa Heads are taken from an ancient Pagan site but they complement the pillars very beautifully and add a different taste to the building. Because of its magic atmosphere and great acoustics, this cistern is now hosting many Classical Music Concerts. There is also a little café which one can sip his or her coffee and enjoy this unique building. On the way to the exit, there are two small bookshops which is full of postcards and informative books as well as some silver jewelry.