It is inaccessible to dreamers under third sphere.
The monstrous wave of consciousness slammed through the Dream, blowing through the portals and rushing toward Threshold. Dreamers caught by it's sudden onslaught were also utterly slain, their very souls shredded by the waves of raw psychic essence! The wave hit the Houses and even their mighty walls could not hold it back. It reached Sanctuary and wiped through it before the screams could even take the air.
Within a period of minutes, every single Dreamer in the city was utterly slain.
The city itself began to spread and shake as the Dorsal Rift grew. Alerted to the disaster while in the waking world, the remaining Dreamers and Master Dreamwrights entered the Dream. There they found utter carnage; the Dreamstate rippled with raw uncontrolled power and the death essences of Dreamer and Mare alike littered the lands.
Fighting the continuing waves of consciousness, every surviving Master Dreamwright - the last of their kind - gathered and forced their way outward toward the Dorsal Rift. Among them were FreeSoul, Illuminate and Freespirit alike, joined in a last-ditch effort to save Underlight. The City was quickly being pulled apart and would soon lose all cohesion if the rift wasn't closed. Arriving at the Dorsal Rift, the Master Dreamwrights found a massive gape in the City, and beyond it roiling and angry chaos. All that had been accomplished in the Dream since it's first day was on the verge of being lost.
The Master Dreamwrights did as their fellows the Overscanners had done that very day... they formed a group meditation and began to focus on the rift. They reached out, pulling at the edges of the rift as they strengthened the city walls. With a heroic effort of will, this group of Master Dreamwrights stopped the Dorsal Rift from spreading and began to pull it closed. For hours they labored to gain control of it, pulling it tighter and tighter, until the moment came when they might completely seal it. It was in that moment that they were lost.
Again the Master Dreamwrights had failed to understand the ways in which exterior pressures bear down on the city. In the moment they made their last thrust to close the Dorsal Rift, a second rift blew open in the exact opposite side of the city... and the Caudal Rift was born. A second wave of consciousness erupted from it, this one crashing down the lands, through Threshold, and straight into the Dorsal Rift. The Master Dreamwrights who had nearly succeeded in closing the Dorsal Rift were caught up and destroyed, their psyches ripped apart and blasted out of the city. This wave of consciousness, while somewhat smaller than the first, was just as deadly to the Dreamers caught in its path. Large teams of Dreamers, at work collecting the essence of their slain comrades and trying to repair damage done were caught in this second wave and slain.