Thremyr's Shield is a vast polar ice shelf that stretches southward from the continent of the Crown of the World from Almhult to the Gulf of Khorkii, covering much of the water between it and Arcadia. It divides the Steaming Sea off the coast of Avistan from the Songil Sea by Tian Xia for most of the year. It is named for Thremyr, the god of the frost giants.
Thremyr's Shield extends hundreds of miles south from the Crown of the World, its ice well over 1,000 feet in thickness where it meets the coast. Even in the brief arctic summer, the ice completely covers much of the coastline. Icebergs calve off the ice shelf year-round. Trelheim Point, a peninsula jutting off the mainland, lies partially underneath Thremyr's Shield.