VARNs (Vehicular Astropod Research Nacelle) are large, slab-like bodies created by the Ancients through 'elemental manipulation' (more detail on this can be found in the History of CRON) for the purpose of experimentation. The worlds were populated and then sent out through the void to fulfill their purpose.
VARN-4 was the setting of Might and Magic I: Secret of the Inner Sanctum and makes a reappearance in Might and Magic VI: The Mandate of Heaven. VARN-6 was a VARN destroyed by Sheltem the Dark by sending it into the sun shortly after Sheltem's Jailbreak. CRON is another world, existing on the same spacecraft as VARN-4.
Might and Magic I
Map of the World of VARN.
The game centers around six adventurers who are attempting to discover an artifact, something of a 'holy grail' within the sanctum of VARN-4. They encounter the Ancients for the first time when they discover a crashed spaceship, and are told by the 'aliens' that their prisoner had escaped. Thus, they enter the plot as Corak hunts for the villain Sheltem, who is discovered by the heroes to be masquerading as the King. At the end of the game, they go through "gates to another world" to CRON, not knowing that Sheltem has travelled there also.
The purpose of VARN to the ancients is unknown; however, as it has the Gates to Another World, which are connected to CRON, it might be a support vehicle for the bigger nacelle.
Might and Magic VI
The term VARN makes a reappearance in the Tomb of VARN, the largest dungeon of Might and Magic VI, where the heroes attempt to recover the VARN control cube that was taken by invaders when the King of VARN was defeated. The Tomb takes the shape of a large Egyptian pyramid, complete with glyphically encrypted stories of the the Ancients and the fallen spaceship that brought them to Enroth.
Might & Magic: Heroes VI
The map reappeared as "A princess of VARN"[1].