Sunken underneath the earths of Vlos’Eairthil lays the drow’s city known as Erelhei-Cinlu. This grand capitol to the Underdark was created to show the power and grasp that the Drow have over the surface world and its inhabitants while still preserving their light-sensitive lifestyle. Hundreds of years ago, this city was literally dropped beneath the earth, thanks to the engineering genius of the Duergar and the arcane power of the Drow. While this finally gave the dark elves a place worthy of their stature, it left a crater more than triple the size of the city.
Destruction and death erupted nearly half way across the lands, demolishing caverns within the Breach, toppling buildings of villages and towns, and even throwing a great tidal wave that wiped out several islands. Not only that, but the towns that were caught within the circumference of the crater were pulled into the Underdark as well, though the ones that were lucky enough not to make it completely through were stuck within the earth. Those that were unlucky enough, however, were dropped into the Underdark and found themselves at the mercy of the Drow, Duergar, and the many other evil creatures that inhabit the world.
Now the crater is a place of unlife: nothing grows in this dark land. There is a continual cloud of dust and soot block out the sun. There is no plant life and therefore no reason for animals to travel. The ground is hot due to the residual power caused from when the earth was turned, making it very painful to traverse the land. The inhospitable conditions, along with the Drow being the main cause of the destruction, are why this area has been given the title Demonweb Crater.