Gunkanjima (also known as Hashima) means "Battleship Island", because the silhouette of its deserted buildings looks like a battleship. Once a significant undersea coal mine, the island supported a thriving, high density population with apartments, schools and shops.
When the coal reserves ran out in 1974, the mine was shut down and the metropolis on top of it was quickly abandoned. It was designated a World Heritage Site in 2015. You can visit this eerie island on one of the daily ferry tours from Nagasaki port.