The Great Falls
A huge set of waterfalls at one edge of the world (near Flotsam) where the ocean flows over th side of the world. This essentially has one ocean flow into the other. The ride is akin to falling but the strange gravity on the edge makes the trip navigable in large rafts tethered to balloons and inflatable bladders. Bloody dangerous though.
The water is returned via the subduction of the Vortex.