Once the most densely populated place in the world, this island is now a ghost town. The tiny, fortress-like island (also known as Hashima, or Battleship Island) sits just off the coast of Nagasaki. Surrounded by a seawall, covered in densely packed buildings, it is completely abandoned – a ghost town that has been completely uninhabited for over forty years. In the early 1900s, Gunkanjima was developed by the Mitsubishi Corporation, which believed – correctly – that the island sat on a rich underwater coal deposit. Over the next nearly a century, the mine grew deeper and longer, extending beneath the seabed to extract the coal that fueled Japan’s industrial expansion. By 1941, the island, less than one square kilometer in area, was producing 400,000 tons of coal a year. And many of those working in the underwater mine were forced laborers from Korea.

Even more remarkable than the mine was the town that grew up around it. To house the miners, ten-story apartment complexes were built on the tiny rock face, a high-rise maze of interconnected courtyards, corridors, and stairways. There were schools, restaurants, and gambling houses, surrounded by a protective seawall. The island became known as Midori nashi Shima, the “island without greenery.” Amazingly, by the mid-1950s, it had a population of almost 6,000, giving it the highest population density the world had ever known. And then the coal ran out.

Mitsubishi closed the mine, everyone left, and this island town was abandoned, left to return to nature. The apartments began to crumble, and for the first time, greenery began to grow in the empty yards. Broken glass and old newspapers scattered across the streets. The sea breeze whistled through the windows. Now, 50 years later, the island is exactly as it was just after Mitsubishi left. A ghost town in the middle of the sea. This unique setting with its mysterious aura has been used in many feature films, especially its use in the 2012 James Bond film Skyfall, which made it known to a wider audience.

From 1974 to 2009, the island was officially closed to all visitors, but recently the intriguing place was reopened for organized tours. The site was approved for inclusion on the UNESCO World Heritage List on July 5, 2015.