Lunopause
The Lung Archipelago is surrounded by a magical, physically impenetrable barrier known as the Lunopause.
It extends about 80 kilometers from the shores in a circle around the island. From outside the circle looking in towards the islands, it appears to be a powerful storm at sea, with whipping rains, dark black clouds, lightning and powerful tornados and vortices. It is invisible looking out from the islands.
Shun He, aboard his magical junk the Lungcao, was the first human to break through it from the outside.