High Magic (WAR History and Lore)  

There are two reported coordinates for the location of the Mage Stone, which is used for triggering this unlock. They are both located in the same area along the ledge, one at 18.6k/19.8k and the other at 17.9k/20.4k. These two locales are very close together, so if you have trouble locating the stone in one, check the other!

History & Lore in Ellyrion