Eberron - Return of the Lich Queen
The Eldeen Reaches are bordered by Lake Galifar and The Wynarn River in the east, Silver Lake in the south, Byeshk Mountains in the southwest, Shadowcrag Mountains and Ice Horn Mountains in the northwest and Eldeen Bay in the northeast. The Demon Wastes border the northwest, Aundair on the eastern border, Breland on the southeast, and Droaam and The Shadow Marches to the southwest. Though the Lightning Rail does not pass through the Eldeen Reaches, House Orien roadways pass through the lower southeast of the nation, around Lake Galifar.
For more info: Eberron Wiki