Korean men were forced to labor over 12 hours a day in these narrow tunnels and shafts.
Being an undersea coal mine, it was prone to sea-water flooding and gas leaks,
which led to devastating accidents. The average temperature inside the shafts was 113°F, and
the humidity often exceeded 95%. While mining, the laborers wore only fundoshi,
a traditional Japanese undergarment that resembled underwear and covered very little of the body.