The Hinterlands is the pocket dimension of the Golden Dragon, Zanzook. The dragon was banished to this dimension by Orva the Red and Vano the Flying Shadow. Zook put it on himself to protect a small city in Reah. The siblings Orva and Vano despised the noble dragon and therefore, worked together to send him away for good.
The dimension is a large island, seemingly ripped from the ground, floating in space. When Zook was sent there, the land was untouched. Thick swaths of trees and a large rocky hill where the gold dragon sat upon. The crew of the Fiddler's Green found the island and the dragon, who was now slightly mad. The combined efforts of Zook and the crew built the island to be more comfortable. A large lighthouse was built upon the hill that served as the dragons lair. They also built several cabins for when the crew was visiting.
The crew of the Fiddler's Green is able to come and go as they please as they were not banished. Zook, however, is locked to the realm. Only if the two dragons that sent him there are killed, will he be able to return to the mortal plane. Zook can still scry through the dimension, so he spends his time finding monstrosities and setting bounties on their heads.