The Frozen Sea
The Frozen Sea is the most northern body of water in perhaps this entire world.  Even when the Northern Glacier stops, the Frozen Sea continues northward.  Few sailors travel these waters even in the summer time, and none may travel it in the deep cold of winter when the ice becomes one with the Glacier.  Ships trapped in these waters when they freeze are ripped to their planks and death is nearly instant to anyone who is touched by these frigid waters.
Anyone who dares to travel the Frozen Sea, even in good summer weather when the sea is thawed, will most likely find themselves face to face with Argen, King of the Ice Dragons.  He fiercely protects this entire region, having led this small band of dragons out of their homeland, and refuses to let any of his Ice Dragons be captured by trainers.