This achievement is the second part of Pursuits: Subversion.
It's currently unknown how to get INSIDE the tower as an order player.
If you have completed the first step of this pursuit achievement, then you will be inside a tower on the hill near Salzenmund. To get out, you must ascend to the top floor where there is a portal device. On that floor you will find Heironymous of Nuln, a level 9 Bright Wizard Hero. Killing him will unlock this achievement. Using the portal will teleport you to the southernmost part of Salzenmund on the shoreline.