Ada Kaleh was a small island on the Danube in what is modern Romania, populated mostly by Turks, that was submerged during the construction of the Iron Gates hydroelectric plant in 1970. The island was about 3 kilometres downstream from Orșova and was less than two kilometers long and approximately half a kilometer wide.
The isle of Ada Kaleh is probably the most evocative victim of the Iron Gate dam's construction. Once an Ottoman Turkish exclave that changed hands multiple times in the 18th and 19th centuries, it had a mosque and numerous twisting alleys, and was known as a free port and a smuggler's nest. The existence of Ada Kaleh was overlooked at the 1878 Congress of Berlin peace talks surrounding the Russo-Turkish War, known in Romania as the War of Independence, which allowed it to remain a de jure possession of the Ottoman Sultan until 1923.
Wikipedia https://en.wikipedia.org/wiki/Ada_Kaleh
Address Romania
Coordinates 44°42'59.997" N 22°26'60" E