Book 5: The Peak Of Life!
The Wildlands were huge, so huge that few people even knew their true extent. However, most cultivators who understood a thing or two about them were able to guess.
If the entire world were circular, then the Heavenspan Sea would be in the very middle, with four enormous rivers stretching out from it in each of the cardinal directions. The tributaries, streams and even the deltas were all like tree branches that grew out from the rivers.
The areas in which the Heavenspan River existed were the Heavenspan Realm. The places where that river didn't exist occupied roughly half of the 'circle' that made up the world. And those locations were known as... the Wildlands.
There was even a well-known saying: Everything beyond the Great Wall is the Wildlands!