Gunkanjima: Anatomy of an Abandoned Coal City

Fifteen kilometers off the coast of Nagasaki, a low gray silhouette breaks the surface of the East China Sea. From a distance its jagged outline of stacked concrete and collapsing walls looks unmistakably nautical, which is exactly why the Japanese nicknamed it Gunkanjima — Battleship Island. Its official name is Hashima, and for nearly nine decades it was one of the most densely populated and industrially productive square kilometers on Earth. Today it is empty, structurally failing, and one of the strangest UNESCO World Heritage sites in existence.

A Reef Turned Into an Island

Hashima did not start out as an engineering marvel. It began as a small reef in Nagasaki Bay, barely large enough to notice, until coal was discovered beneath it around 1810. Mitsubishi bought the rock outright in 1890 and began undersea mining in 1887, then spent the next several decades physically enlarging the islet with a sequence of land reclamations and reinforced sea walls to hold back typhoon swells. By the time the walls were finished, Hashima measured roughly 6.3 hectares — about 0.063 square kilometers, or the footprint of a few city blocks — entirely artificial at its edges and entirely given over to the business of extracting coal from shafts that ran more than 600 meters under the seabed.

Between 1891 and 1974, an estimated 15.7 million tons of coal came out of those shafts, feeding the furnaces of Japan's rapid industrialization, including the Mitsubishi shipyards that built much of the country's modern navy and merchant fleet.

The Densest Address on Earth

To house the workforce on so little usable land, Mitsubishi built up rather than out. In 1916 the company completed a seven-story reinforced-concrete apartment block on the island — widely cited as Japan's first large building of its kind — and kept building for decades afterward, packing in schools, a hospital, a cinema, a Shinto shrine, shops, and rooftop gardens meant to give residents a sliver of green amid the concrete. Corridors connected some buildings directly so residents could avoid the wind and rain of typhoon season entirely.

The result was crowding almost without precedent. In 1959, Hashima's population peaked at 5,259 residents living on that same 6.3-hectare footprint — a density of about 835 people per hectare, or roughly 83,600 people per square kilometer. For comparison, that is several times denser than even the most crowded wards of modern Tokyo. Families lived in single rooms as small as ten square meters, sharing the island's few communal spaces with thousands of neighbors, miners, and their children, all within a few hundred meters of the mine shafts they worked.

Coal, Concrete, and Forced Labor

The island's productivity came at a documented human cost that Japan has only partially acknowledged. During the Pacific War, Mitsubishi conscripted Korean laborers and, later, Chinese prisoners of war to work the Hashima mines under brutal conditions, alongside Japanese miners who were free to keep their wages and papers. Forced laborers were not. Historical accounts describe workers so desperate to leave that some attempted to swim the roughly 18 kilometers to the mainland; drownings among escapees were documented. In a 1973 interview, a former mine supervisor, Masayuki Kosako, acknowledged that Chinese and Korean workers were treated differently from Japanese employees and that some "drowned while trying to run away."

That history became the center of an international dispute in 2015, when Hashima was inscribed on UNESCO's World Heritage list as part of the Sites of Japan's Meiji Industrial Revolution. South Korea objected strenuously to including a forced-labor site without acknowledgment, and Japan's delegation publicly committed to presenting the full history, including that workers were "forced to work under harsh conditions" at several of the listed sites. Critics — including South Korea's government and multiple historians — say Japan has since fallen short of that pledge; an information center opened in Tokyo in 2020 to interpret the sites was criticized for downplaying or omitting survivor testimony about coercion and mistreatment.

The Mine Closes, the Island Empties

Hashima's undoing came not from the sea or the war but from petroleum. As Japan's energy economy shifted from coal to oil through the 1960s and early 1970s, the mine became uneconomical. Mitsubishi closed it in January 1974, and the effect on the island was immediate and total: residents began leaving en masse, and by April 20, 1974, the last inhabitants had departed. A city that had housed thousands a few years earlier was, within months, completely empty — furniture, schoolbooks, and televisions left behind in apartments that no one would occupy again.

For 35 years Hashima sat off-limits, battered by salt air and typhoons, its unreinforced interior floors and stairways gradually collapsing while its concrete shells remained eerily intact from a distance. Photographers and urban explorers who reached it illegally in the 1990s and 2000s produced the first widely circulated images of the ghost city, feeding a growing international fascination with the island as one of the world's most photogenic ruins.

From Ghost Island to World Heritage Site

Limited legal tourism began on April 22, 2009, when Nagasaki City opened a small section of the island to visitors on guided walkways, keeping most of the crumbling apartment blocks fenced off for safety. The island's stark, decaying skyline has since become a fixture of popular culture — its silhouette inspired the villain's abandoned island lair in the 2012 James Bond film Skyfall, and it has appeared in the live-action Attack on Titan films.

What tourists see today is a monument to contradiction: a site that represents both a genuine feat of early twentieth-century engineering — undersea mining, reinforced concrete construction, and a self-contained urban ecosystem built on a rock in the open ocean — and a site of coerced wartime labor whose full history Japan and its neighbors still dispute. Hashima's concrete towers, half-collapsed and salt-eaten, are not simply photogenic ruins. They are the physical remainder of a 20th-century industrial experiment: how many people, and how much extraction, could be packed onto the smallest possible footprint of land — and what happens to all of it, all at once, when the reason for its existence disappears.