Diadem

Diadem is a world "mirrored", believed to be the pure form of the world that dwells below it. The lower world, known as Sonder to its natives, is strictly forbidden to travel to, and it is considered a death sentence if one chooses to do so.   Criminals accused of treason and heresy are often banished to this lower world with the assumption that death will rightfully come to them, whether it is by entering the world itself or by succumbing to the supposed horrors that lurk there. Unbeknownst to Diadem's natives, the horrors of Sonder are sparse, bordering on nonexistent, as it has functioned as no more than a wasteland since it was abandoned by a ruler of Diadem more than five hundred years ago and branded as an impure version of Diadem itself.   Any means of traveling to Sonder legally were cut off when Diadem abandoned it, forcing those who chose to travel back and forth between the worlds to forge a new, secret path: Anemone, or the world tunnel. Anemone itself houses upwards of a thousand homeless citizens of Diadem and refugees, those forsaken by Diadem who managed to escape before their banishment, and those from Sonder who traveled there in search for an escape from the wasteland.