Valley of Screams

The is a dimension that forms between the Human World and the Soul Society, stemmed from the Dangai.

Overview
Its appearance is a regular occurrence that happens naturally due to souls getting lost trying to get to Soul Society and as such, can only be accessed from the Human World. The valley bears a resemblance to the underground Training Area created by Kisuke Urahara, only the size of it is on a worldly scale. The valley is primarily a rocky area with many canyons and mountains.

Blanks resided in this place, separated from their memories, until they come in contact with the Shinenju. Subsequent to their expulsion from Soul Society, the Dark Ones claimed this to be their homeland until they would invade Soul Society and take their revenge.

The Valley of Screams eventually expands to a point where it connects Soul Society and the Human World. The Dark Ones attempt to collapse this dimension in order to force Soul Society and the Human World to collide. This collision would have resulted in the destruction of both, fulfilling their need to gain revenge for their exile over a millennium prior.