Sand giants are a species of humongous creatures of apparently humanoid build. It is implied that the giants are a very old race, and that they have always been blind, but possess good hearing. Their amygdala have eye-sight enhancing properties, and allow the person who eats them to see through the mist.
The fog folk has buried a sand giant in the deep fog trench. They warn the player not to go see the giant, implying they feel it poses a hazard. The giant is alive, as evidenced by the fact that the sound of the horn made it rise its head above the surface.