The Endless River is the longest river in Highpoint. It runs east to west across much of the continent, however most of its course is underground. It can be accessed at several points along the Endless planes, and shows up briefly at Edge in the form of a great waterfall. It then travels most of the way across the rest of continent submerged, and only immerges to run across the Wet Desert.
These traders are masters of traveling up and down the Endless River. There are claims that they are magical. Its difficult to say