Here are the quests you need to complete to get there. The Arathor Courier's Satchel can be found in the zone of Hallowfall, and only takes a bit of flying to get there. With this guide in-hand ...

From here, you can also fly to the other two zones, Hallowfall and Azj-Kahet, though the paths to these are easily discernible with a look at your map. Just remember that enemies won't necessarily ...