The Shadow Zone
Within the Nexus, there are plenty of dimensional planes; some are nonmaterial, like the Astral and Mental planes, some are purely digital, like the Datastream, and some are entirely within the Material Realm. Like a Planet existing within the gravity well of a solar system, or a town living within the boundaries of a city, the Material Plane can, in turn, be divided into various layers, the very top of which encompasses everything that exists within the Nexus at large. Enveloping all 10 CTMs of diameter that make up her borders. But what do we call this top layer from which everything within the Nexus is located within? The Answer is rather simple actually. In fact you have already passed through this domain at least once on your journey here, we call this domain of existence,The Shadow Zone.
At first glance, it might seem like the Shadow Zone is utterly devoid of any typical geographical features. After all, the Shadow Zone is effectively just a much fancier version of outer space. But anyone who has explored outside their homeworld will tell you that outer space isn't exactly as empty as it may seem at first glance, and the shadow zone is no exception to this. Explore the vast expanse long enough, and you'll find various structures floating silently in the void. Some of these structures are entirely in use today, like the Main Hub and the various outreach outposts ran by the PKT, the MDA, and The Collective, while others seem to have fallen to ruin, abandoned millennia back. At the center of the Shadow Zone, one can find a glowing blue light coming from the Tower in the Epicenter, shining as bright as the sun does for the earth, fully visible even as far out as the Institute and the Abandoned Lab of Ancients.
Given the fact the Shadow Zone is entirely a vacuum, you would assume that there would be no ecosystem that could even take root inside it, and in a way, you would be right. No typical ecosystem could ever survive the harsh vacuum of space. Under ordinary circumstances, that is, but the metaverse is anything but ordinary. The Shadow Zone may seem cold and desolate today, but recently dug-up records hint that long ago, life may have somehow managed to take root even here. Sadly, I am afraid we can only speculate on what form this life took and what their properties were, as there seem to be little to no traces of their presence that persist to this day.
While traveling within the shadow zone, one will notice a few different effects that seem to occur to those who travel it. For one, Time seems to work very differently within the Shadow Zone than inside the various Realms within it. However, this might be the relativistic forces that are inevitably invoked due to how fast one must go to travel the distances within the Shadow Zone in any reasonable amount of Time. There is another phenomenon to mention, though it only happens once every few eons. The realms within the Shadow Zone are not stationary; they constantly orbit the Tower like planets orbiting a star. Once every few eons, all the realms align perfectly with the Tower creating an astrological event known as the Convergence. During this alignment period, the laws of reality seem to descend into chaos, allowing things that should not be possible to become inevitable to occur. Or at least that's how it would seem to the casual observer. A third well-known phenomenon would be the "Highways" that are used primarily by those traversing the expanse, regions of altered subspace that allow for accelerated travel between the Main Hub and the various realms within the Nexus.
Due to the fact, the Shadow Zone is a vacuum containing no atmosphere, it does not have any climate to speak of. There aren't even solar phenomena that would typically occur, as there are no stars in this void to create such an event.
It is not entirely clear when the Shadow Zone was first discovered, as every civilization that has found the expanse seems to lay claim to being the first to uncover its existence. That being said, one organization holds the most credible claim for being the first to discover the Shadow Zone. Given the Collective's reach even back in the 1st Era, it's very likely they were the very first to discover its existence, though with Merlin's return 70 years back, even that claim is now being called into question.
While the Shadow Zone does not have a tourism presence in the typical sense, there is no questioning the fact that the Shadow Zone serves as the defacto transport hub for all civilizations and groups that have managed to access it. Inter-realm travel would be impossible without using the "highways" present within the Shadow Zone to travel between the various realms.