The Lost Lands is a large portion of western Arad, once known as Aetgard. When the Great Plague struck and Aetgard's human population was almost completely wiped out, the region became known as the Lost Lands.
It has been over one hundred years since the Plague struck, and the human population has recovered somewhat since then. There are a number of towns, hamlets, and outposts established in the Northern Lost Lands, while the southern portion is mostly barren save for the kingdom of Lapis, the largest surviving remnant of Aetgard.
The Lost Lands is, like much of western Arad, within the Quarantine.