So here it is.
See atachment.
Yes the grey area at the south is a sunken land. Like a huge swamp. As far as the fantasy is concern it is the land of the orc's clans. In this world the orcs and some elfes was the owners of the world until a major uprising. You find grey orcs (very athletics ones, they climb like monkey and run as fast as well trained horses), draugh (they have a shell all over the body), and common orcs (frenzy ones) here. You can also find forgetten castles and hydras hiding under poisened clouds.