The Yden is the region that lies within the Ydenrim. The Ydenrim is the lip of a submerged, ancient crater. This lip rises some little way above the level of the lake.
Much of the Yden is land which is a result of the subsided ash cone of the volcano of which the Pillar of Heaven is the only remains. The rest of the Yden consists of shallow lagoons whose level is raised by the Ydenrim higher than the surrounding lake.
The diagram shows the Labyrinth which is built on the higher ground that lies between the Pillar of Heaven and the Plain of Thrones. Around the base of the Pillar are the Forbidden Gardens with their terraces. Dotted lines show height contours. Note the wide contour to the northwest (this is clearer on the expanded diagram) which shows the wetlands that slip away into the lagoons.
Also shown is the route taken by Carnelian and Osidian on their first visit to the Yden: from the Quyan Stair, through the Forbidden Garden and down towards the lagoons.