After the Undead Tribe completely occupied the Giant's Ridge Mountains, they began assisting Yinbutu in constructing a new royal palace.
The new palace was chosen to be located between two rivers in the Rolins Forest… One of the major rivers was the border between Yinbutu and Giant Valley.
Logically, the palace shouldn't be built at the border, but for Yinbutu, where most bustling cities are by the sea, this location is most suitable for avoiding the Magicplague.
After all, being surrounded by the forest, and with the two massive rivers from the north and south, plus the Giant's Ridge Mountains to the east, provides innate defense.
Moreover, the palace they chose isn't luxurious; once this disaster ends, they can completely treat this as a forest villa and renovate a new palace on the old site… This is what Queen Yinbutu and the Crown Prince told the restless and discontented King.