A City in the Sea
From afar, Hashima Island looked like a battleship adrift in the East China Sea. Concrete towers crowded the rocky outcrop, encircled by a seawall, rising from the waves 15 kilometers off Nagasaki. At its height in 1959, over 5,000 people lived on its 6.3 hectares, making it one of the densest places ever inhabited.
Beneath the island, a vast network of tunnels reached a kilometer below the sea, where miners extracted coal that fueled Japan’s industrial revolution.
Mitsubishi’s Concrete Fortress
Coal was discovered around 1810, and by 1890 Mitsubishi Goshi Kaisha had purchased the island to mine under the seabed. Over the following decades, the company expanded the island through land reclamation and built reinforced concrete apartment blocks to withstand typhoons.
Japan’s first large concrete structure, a seven-story apartment completed in 1916, stood here. By the 1930s, Hashima had schools, hospitals, shops, rooftop gardens, a cinema, and a swimming pool. Families lived in compact apartments stacked tightly together, with every inch of the island built for function.
Dark Years of Forced Labour
From the 1930s to 1945, during Japan’s wartime mobilization, Korean civilians and Chinese prisoners of war were brought to the island and forced to work in its mines. Conditions underground were brutal, with high heat, humidity, and frequent cave-ins.
Historical accounts record deaths from exhaustion, malnutrition, and accidents. Estimates of the number who died vary between 137 and 1,300. When the war ended, Japanese residents resumed life on the island, and production peaked in the 1950s as coal powered the country’s postwar recovery.
Abandonment and Uneasy Memory
As Japan shifted to petroleum, Mitsubishi closed the mine in 1974. All residents left that same year, and the island stood empty, its buildings left to decay in sea air and typhoon winds. For decades it was off-limits, until tourists were allowed back in 2009.
In 2015, Hashima was inscribed as part of the UNESCO World Heritage Sites of Japan’s Meiji Industrial Revolution, despite objections from South Korea, which demanded acknowledgment of the forced labour history. UNESCO later ruled that Japan’s exhibits at the Industrial Heritage Information Centre failed to meet the agreed requirements to present that history. Disputes continue, as most of the island remains off-limits and its concrete shells crumble by the sea, holding the traces of a once-crowded world now silent.
Off Nagasaki, a concrete island once looked like a battleship and held one of the densest communities on earth.
Beneath it ran deep coal tunnels.
Later came forced labour, a sudden exodus, and a UNESCO debate.
Here is Hashima, from rise to closure to disputes…🧵👇 pic.twitter.com/RO1nreqsRv
— Fascinating True Stories (@FascinatingTrue) November 12, 2025