Otherwise known as 'battleship island,' Hashima is a small island near Nagasaki. It was developed in the early 1900s to mine the coal underneath it and at its height (1959) was one of the most densely populated place on earth. The comment about 'needless deaths' near the end of the movie is a reference to the fact that during World War II the Japanese brought in Koreans and had them mine coal on starvation rations. In 1974 the coal mine was closed and shortly after the island was abandoned. Today, travel to it is prohibited.