The Narrow Sea is a strip of water that divides Araluen from Gallica. Before the treaty with Araluen was made, Skandian wolfships had to cross this sea to raid Araluen and southern lands. In book two, when Will and Cassandra were kidnapped, Erak's wolfship, Wolfwind, had to sail through the Narrow Sea in order to get to Skandia. It may be this story's version of the English Channel.
The streams of the Narrow Sea have caused erosion in the coastline of the Mountains of Rain and Night, and as a product of this made high cliffs around the area.