Songline

The empty spaces between landmasses, they function in similar manners to rivers broadly speaking. The air within is thick with magic, and as such flying and swimming creatures can traverse them. Skyswimmers are the most adept at traversing them and rarely ever stray onto islands. One must be careful on the edge of land however, as the songline doesn't start in any substantial way until one is about 30 feet away from the land. If you walk off the edge without getting over that gap, you'll fall to the World Before.