Kairoseki Island is the central mining facility of the Marines and World Government of Kairoseki, it is also known to be a prison of Devil Fruit pirates with a bounty of 500,000,000beli or more. As the central hub for keeping dangerous devil fruit users under watch, it is rumored to have the most powerful Devil fruits kept there. While the island it self is relatively small the island connects miles down to the sea floor where all mining activates take place. The island is most identifiable by the incredibly large kairoseki tower in the center.