Hashima is a small island located off the coast of Nagasaki. Between 1869 and 1974 it produced large quantities of coal for Japan, rising to 150,000 tons in 1916 and peaked at 410,000 tons in 1941. Because of the limited area available on the island it had to import most of its resources from mainland Japan and at one point it was the most densely populated area in history. More here.