The Great Expanse is north of High Wood Country and the Tribe Steppes. Three seas border this region; west lies Nielalroch, northeast is Edhelviel, and northwest is Nautrek. The northwestern coasts of the Great Expanse are nearly perpetually covered in fog. This is attributed to the joining of the warm water of Edhelviel with the cold seas of Nautrek.
Before the arrival of the Gear Monument, the Great Expanse was a wild region of trackless plains, deserts, savannah, and tundra. It was largely uninhabited by intelligent humanoid civilizations. This changed when the Gear Monument began to produce machines, like maugs and warforged. As the years passed, these living constructs produced more of their kind, and have come to dominate the Great Expanse.
In addition to the living constructs, thri-kreen can be found in great numbers in this region. Along the northern coasts of the Great Expanse are rolling hills and verdant rain forests. In these northern reaches are halfling states. They are concentrated in an area called the Seven Vales of the Hairfoots.
The Underdark region beneath the Great Expanse is called Uddring.