The Mainland is a region near the center of the set of islands called the Lands of the Founder, which is known for its wildly differing climates on such a comparably small landmass.
The northern reaches of the Mainland are covered in snow and ice, and in addition, the eastern half of the north is also covered in swamps and forests of rotted wood. These northern reaches used to be two different countries: Zariaha and Witherwood, until Zariaha offered Witherwood protectorate status in the Year 3024 of the Third Age, and ultimately annexed Witherwood into Zariaha, creating the District of Witherwood within the Zariahan Empire.
The central regions of the Mainland consist of the Westerlands, which before the Year 3024, was under the control of the Westerland Empire, until Zariaha conquered it; the Deep Woods, which is far to the east of the Westerlands, whose territory is considered neutral; and the area between the two, now known as the Pits.
Lastly, the southern Mainland, there are, again, three regions. Firstly, to the west, and south of the Westerlands, there is the Sandscarian Desert, whose main settlement is the mining town of Sandscar, who, itself, is part of the Zariahan Empire. Secondly, is the Kotanian Jungle, which is under the control of Agdruzalian Kokura's Rift, which was previously, mostly, uninhabited, except for the island town of Kotana, off the southern coast. Lastly, to the east we have the Rift. The Rift, as a result of the War of 3024, is being governed by the Dwarven-Elven Coalition.
On top of this, mountain ranges act as pseudo borders between most of the regions.
At its two farthest points, from the east to the west, the Mainland is 5178 km wide.
Overall, it's a diverse, yet separate place, filled with many people of different stripes.