At the end of the River Iss surrounding the lost sea of Korus is the Valley Dor. A lush and fertile place, it is filled with thriving plant life, songless birds, and some of the most feared predators upon the entirety of Barsoom. Here is where the plant men live alongside the great white apes. Anyone who takes the pilgrimage down the river of mystery is met by the combined forces of these predators. If they do not meet their death at the hands of either beast they are enslaved by the Therns who inhabit the walls of the valley, and the greater valley that surrounds it.