Rift Quest:The Towers Ablaze  

Head to the Iron Fortress by following the road leading southwest from Denegar's Stand. This main road will lead directly into the fortress. The first alter can be found at the top of the tower that you enter the fortress from. Interact with it to destroy it. The second and third alters are located at the top of the eastern and the western towers respectively. You can follow the ramparts to the towers or cut across the courtyard. The ramparts appear to be slightly easier to manage if you are doing this solo.

Once you have destroyed the first three alters the quest will update and ask you to destroy Jakub's alter. This alter it located at the top of (you guessed it) the north tower. Destroy this alter and then interact with it once more to complete the quest and start the next quest in the series.