Mountains of the Sky

The immense natural wonder known as the 'Mountains of the Sky' is visible for vast distances, as it stretches high into the sky in a column of floating rocks. In existence for the past thousand years, it was formed in the aftermath of The Sundering when the main continent was smashed.
The site was the location of an elven experiment in gaining additional magical power. When the experiment backfired catastrophically, the surrounding region was smashed to rubble and the outlying areas into scattered islands. As the magical cataclysm continued, fundamental forces like gravity were affected in strange ways, and massive chunks of stone were plucked free of the in-rushing sea and hurled into the air. Eventually the magical side effects stabilised, but after-effects like the altered gravity remained locked into the fabric of reality.
The rocks float freely, but only move a short distance before returning to their point of origin. The column stretches far into the heavens, and aurorae have been seen to play around its top, when researchers have tried to scry or use carefully polished telescopes to try and ascertain how far up it goes. Attempts to study it more closely are always foiled by the wild dragons that roost upon the rocks.
The dragons are not as intelligent as humans and cannot speak any known language, even when magically-assisted attempts have been made to communicate with them. At certain times of the year, as bolts of magical lightning arc between the massive stones, the dragons become agitated and fly around the column in unison, vast spirals sweeping up into the sky and then back down. Nobody has been able to ascertain what causes this behaviour or the magical discharges.
On several occasions, magical discharges, lightning, and aurorae have all happened at the same time. As sheets of flame roar across the heavens, the Mountains of the Sky turn into a burning column thrusting from the ocean to impale the sky, with shadowy outlines of dragons circling around it for those close enough - and brave or foolhardy enough - to watch.