Underdark

The Underdark is a series of tunnels and caverns underneath the surface of Felidra, so extensive that it is it's own geographical and political system. It is divided into seven regions, which do not represent political alliances but general physical attributes. These regions are The Barrow, The Heartstone, The Depths, Border-North, The Burning Grounds, The Sunken Sea, and The Southern Reaches.
Many people on the surface consider the people of the Underdark to be somewhat backwards, in that most Underdark cultures draw along racial lines, whereas few places on the surface continue to do so.