Empire of Mordor

"One does not simply walk into Mordor. It's black gates are gaurded by more than just orcs.  There is evil there that does not sleep, and the power of Sauron is ever watchful.  It is a barren wastland, riddled with fire and ash and dust.  The very air you breathe is a nearly poisonous fume."

Boromir at the council of Osgiliath

Mordor is the realm of Sauron. It resides directly east of Gondor.