Tyelcirion is a deep canyon of the Pearl Sea's hadal zone. In one part it is nearly 40,000' deep. The area is rife with geothermal activity, with underwater vents, and several growing volcanoes. A few of these are close to the surface, hazards to ships when steam blasts over a wide area, or massive rocks and streams of lava blow the surface. Though the dangers are high on the surface, underwater is like an eden with many schools of fish, some so large that they blacken the areas beneath in shadow. Away from the stream of lava and chemical laden spouts, there are towering forests of kelp and vegetation so expansive that entering them is like going into a surface forest.
In the Durkoth Descent (995 HE - 1355 HE), around 1150 HE, Durkoth began coming to this area. They were those that had mutated into something more aquatic. Most of them had once had homes in Nagdúrzol. Over the next decade they began their subjugation of the the area's merfolk. For two centuries, ending with the onset of Thyrms Breath, these merfolk were under Durkoth overlords. It was a harsh time, with children separated at birth, raised in a crèche for a specific task. The merfolk of Tyelcirion are scarred from this time. They are chaotic, destructive and evil natured, "equal to the sahuagin in their viciousness."