This is Hashima 端島, the infamous undersea coal mine just off the coast of Nagasaki Peninsula. The island is also known as Gunkanjima (軍艦島 or Battleship Island). The mine was owned and operated by Mitsubishi until its closure in 1974. It is visible from most viewpoints up and down the coast.

More information about the appalling history of this island can be found on Wikipedia.