Vel'kira is a large artificial plane, now fragmented.
The first city created was Til'aris, which by necessity had to be anchored to a world around a different star, since Til'raine's was no longer viable. A new ethereal sun was created above Til'aris, so that it might shine down upon the city in eternal day. For a time, inhabitants of Til'aris still called themselves Til'dari, in denial over the loss of their home, but most of the people of Vel'kira were more realistic about it. They called themselves Vel'dari, Children of the Void.
Til'aris was far from the only city. Vel'kira grew vast, with powerful mages carving out cities and kingdoms for themselves. Magic was thrown about freely, and the Vel'dari creators wielded near-godlike power. Each little kingdom operated by its own rules, even though most paid lip service to the Vel'kiran Empire. Some tolerated mutants or even embraced them, others rejected or even killed them. Some liked magic, some hated it, some banned it from all but the ruling god-mage.
Each city held vastly different landscapes, although most had an artificial sun of some sort. Some had orbs of fire or light that rotated around the city and passed through holes in the ground, mimicking the world of Til'raine. Others were more realistic about the fact that they were no longer on a planet. They held aloft giant lamps into the air, one or more of them, or simply had many, many lamps at street level. But for the most part, the Vel'dari acknowledged they would never have the sun again.
The Vel'kiran Empire made up much of Vel'kira, and connected each city with a Nexus that allowed teleportation to any other Nexus, thereby linking most of the cities together despite vast distances of open wilderness or empty planes between them. Some areas held themselves independent, and had no Nexus, or were simply small, outlying towns increasingly far away from the main cities. The most extreme of this was Dis, which bore no sun at all, but four 'moons' that gave off little light.
Vel'kira was unstable from the moment it was created, and only the power and skill of the god-mages held it together. But their focus on their own territories left the areas between the city-kingdoms weakest. Ultimately, their power waned and they died or isolated themselves one by one. Vel'kira might have still persisted regardless if it weren't for one of them deciding to continue experiments with Void Magic. These experiments were the last straw on the stresses against the plane, and wound up tearing it apart.
Realizing that their creation was fragmenting, the surviving god-mages worked to save it or fled into pocket-worlds that could be maintained more easily. Some, in desperation at failing to stop the collapse of the plane, returned to the Material Plane.
Vel'kira ceased to exist as a single cohesive realm around ten thousand years ago. The surviving fragments, many of them with intact Nexi, remain as the planes.