The Neutral Territories are where Exillium classes take place. One of the Neutral Territories is known to be Brackendale. Calla takes Sophie and Biana there to check on something. The neutral territories were attacked often by the Neverseen's plague in book four.
Neutral territories include Wildwood, Bosk Gorge, Merrowmarsh, Brackendale, and where the Lake of Blood is.