This is Veldanterra. The most prominent feature of this grandiose city is the floating fortress. A chunk of land floats freely and moves around the city at a height of 500 feet. This is possible thanks to the work of a great wizard ho lived 200 years ago, he created a complex apparatus which uses affinity stones attuned to the Elemental Plane of Air. This creates a connection with the raw energy from that plane that allows the castle to float.
Something has gone amiss recently, however. The castle is slowly but steadily losing height. People fear it may well crash into the city if no one stops this. The current court wizard is a great magic user but largely ignorant of elemental magic and the places. Even he does not know why the ancient device is failing.