During your exploration of the game world, you encounter many strong opponents, who are not that easy to defeat. Among these elite opponents, great dragons deserve a separate mention, especially that tracking down and killing these beasts, is rewarded with an achievement. Below, you can find information about the dens of great dragons. The descriptions of the localizations of each individual dragon are provided with the number of the map, in the walkthrough, and the name of the quest, in which it is best to find the den.
The first of the great dragons is Cail the Silent. You find the beast in Searing Falls (M26,1), i.e. the small location to the east of Defiance Bay. It is best to attack the dragon during the Cinders of Faith quest, which you receive from Fyrga in First Fires (M22,4).
The second of the great dragons is the Adra Dragon. He is staying at the lowest, fifteenth, level of the Endless Paths of Od Nua (M55,2), i.e. the vast dungeons underneath the Caed Nua Keep. It is best to attack this dragon, while completing The Master Below side quest that you receive from the Steward in the keep' main hall (M13,1).
The third one of the great dragons is the Sky Dragon. You find him in the large nest in the Temple of Hylea (M58,2), i.e. one of the last locations that you visit during the game, past Twin Elms. The best moment to attack this dragon is during the quest from goddess Hylea - The Nest Above the Clouds.