Osrakum is a crater that contains the Skymere and, in the midst of this lake, the Isle. On the Isle is the smaller crater containing the Plain of Thrones and beyond that the Labyrinth. The Yden forms the greater part of the Isle. From the heart of this rises the Pillar of Heaven hollowed into the summit of which are the Halls of Thunder. The Sacred Wall of the crater has cut into its inner surface the coombs of the Masters and is only fully breached by the Canyon of the Three Gates which leads out to the City at the Gates.