The World Nexus is a dungeon uberquest accessible by using Dark Portal after talking to the Lost Traveler at the end of the Desolate Road. It consists of three levels: the first two, called Nexus Bridge, are relatively small areas that lead to the final level, simply called World Nexus, a black, invisible maze where Atanna Khan rests.
The World Nexus, the dimension between heaven and hell which no one knows how to reach. Here the formerly beautiful daughter of Juris Khan, Atanna, awaits your arrival. While she was able to resist Diablo's influence longer than most, in the end she succumbed and now she is an undead demon at his disposal looking to take her anger out on anyone who stumbles into the world between worlds.