Ferra

Ferra is one of the Throne Worlds - universes existing on a radically higher energy level than the much more common Vassal Worlds. As a result of this, Ferra simply doesn't play according to rules recognizable to inhabitants of more 'natural' planes of existence. In harsher words, it would be nonsensical - if it didn't follow its own rules. It is, however, pretty unique on that level.
To begin with, it started as a world even less soaked in magic than the Vassal Worlds. In fact, it had almost no magic. It, however, climbed all the way into becoming a Throne World through a combination of conscious metaengineering and the Reality Protection Array that has kept it save from external incursions in exchange for continuously cycling magic through it, slowly improving its magic level.
It is also all that remains of the ancient homeworld of Mankind. During the Golden Age of the Dominion the entire Solar System was reshaped in the largest case of reality warp in the history of human metaengineering. The result of the warp was the cessation of existence of the Solar System, and its replacement with the combination of a Dyson Sphere (used to harvest solar energy and then convert it into a unique form of mana, thus acting as an artificial Dark Lord) and a Ringworld that houses the entire population of this realm.

Geography

This world is composed of two things. The first one is the Dyson Sphere encapsulating the Sun and intercepting almost entirety of the light it produces. The Sphere uses the harvested energy for four main things, that remain crucial for the continuous existence of the Multiversal Dominion of Mankind - and are in fact at least partially required for the continued existence of the civilization as we know it.
The first thing is the conversion of solar energy into iron mana, which is then emitted throughout the multiverse. This mana remains the driving power behind all techmaturgic-oriented magic in the multiverse, and powers all the advanced machinery (from the dimensional gates allowing easy travel between the worlds, to the machines of Ferra - including the other elements of the Dyson Sphere.
The second thing is housing the self-repairing, autonomous and entropy-shielded machinery of the System - the multiversal-spanning marvel of metaenginerring that keeps the Dark Lords from resurrecting themselves and purifies their power into various types of mana (save for the iron one) used throughout the multiverse to power up magic, posthumanity evolution into the higher evolutionary stages, and numerous other things.
The third thing is housing and maintanance of the High Overseer, the first among numerous Artificial Intelligences that are not only maintaining the lavish lifestyle of the inhabitants of Ferra, but also its legions of combat machines and the remaining caches of superweapons. It is also suspected that the High Overseer is responsible for continued operations of various bits of techmaturgy that remains active in other universes after the Blackout - such as the machines that keep Nidavellir habitable, and the Panopticon locked down. Other suspect that it's System who's doing that, and High Overseer is mostly sealed after System designated it as a Dark Lord.
The fourth thing is projecting enough light from the outer surface of the Sphere to keep the ringworld habitable. While minor to the multiverse at large, it's vital to the humans of Ferra - and it's not sure if the multiverse is ready for their extinction and the inevitable wars that would follow.
The second half of the Ferra is the ringworld. Lightened up by the limited (and controlled) transparency of Dyson Sphere fragments, it is where Mercury once was, and is as long as its orbit once was - so about 58 000 000 kilometres long. It is an utopia of fully controlled environment surrounding millions of self-contained arcologies housing once human population of this world in truly utopian abundance - so utopian, unfortunately, that almost entire population has long ago lost all interest in what's beyond their homes. They live like gods - and fail to realize their own slow descend into obscurity.