The island is surrounded by a sea of fire on one side and icebergs on the other. In the center, there is a hole where seawater flows into it, which separates both halves of the island and has sharks living within. This hole has fierce wind and currents running across it. As touched upon by Robin, the extreme temperature differences between the ice and magma lead to an equally extreme difference in air pressure, forming massive gale-force winds. The lake was originally a crater formed at the epicenter of Akainu and Aokiji's death match and then later filled with seawater, though the aftermath of the duel did leave behind patches of burning and frozen waters in the lake. The entrance is bolted with a danger sign, hazard stripes, and the logos of the Marines and World Government. The external border is heavily fenced in and inside lies a military base.