The Floating City of Miraa was created by I'noc and Rannoc before they slew one another. Its purpose was twofold: to house the ancient temple ship that monitored the Shardling's growth, and to confine the frost giants' cataclysmic storm to a small area, where it could no longer harm Vallene. The Twin Gods left behind a city populated by creations built to maintain the city which eventually began modifying themselves in order to continue functioning. Their repair protocols left them driven to repair and keep up themselves as well. In modern times, the city was commandeered by Bastion, and used in a series of events which culminated in the storm being eradicated. The process left the city covered in ice, and it has since fallen from the sky and lies on Vallene's surface now.
The ancient temple built prior to Miraa's existence once sat at the peak of the spire in the city center. Inside, a monitoring station mapped Vallene's interior and tracked the growth of the Shardling inside Vallene's core. The temple has since been removed from Miraa, piloted by Avi.