This is the Sankyan Wilderness. If you read Book Two of Melody and the Pier to Forever, you know it moved.
It is central to the entire story arc, as it turns out. This view is an omniscient one that no one in the story has. The Sankyan is a land defined by mystery above all things. The fact that throughout Aquanian history it has regularly moved only adds to that mystery. It doesn't even stay the same shape move to move; and it doesn't even stay the same length of time between each move. It doesn't help that almost every explorer that has attempted to land on its shores has died.
The latest novel in Melody's story arc involves a Saeire Insu warship that must sail around the Sankyan Wilderness' southern tip as it chases an enemy vessel with secrets that could doom the Revolution. I just wrote the part that allowed me, after many years of anxiously waiting, to add the warship's contribution to the war effort. The warship's name is Failure. And its contribution ends up being legendary.
You can view the entire map of Aquanus here.