The city of Istanbul is the Capital of Turkey. It is located on the tiny European part of the country, at the narrow connection between Black Sea and Mediterranean Sea. Here the waterway has a bend which is called the Golden Horn.
The city was founded 600 BC and named Byzantium. It became Roman, grew because of its strategic location, and finally became the second capital of the Roman Empire. It was made the eastern capital by Constantine the Great, and so it was renamed Constantinople. And when the Roman Empire collapsed, it became the capital of the remaining Empire. Later area was ruled by the Ottomans and the name Istanbul was used. The western world still used the name Constantinople, but finally with the establishment of the Turkish Republic, the name became official.
The city has no caves, and underground structures are generally of Roman origin. The city had huge aqueducts and the water was stored in 150 cisterns located all over the city. Originally the Cistern Basilica was the only one recognized by tourists, But during the last 20 years numerous others were renovated and opened to the public, as museums and as art galleries. One is used by a restaurant, another is a private art gallery financed by a carpet store,