What the achievement asks
Complete all 7 storylines of Vol'dun. Ten points, account-wide, Horde only.
There is nothing hidden and nothing timed. This is the zone's own story, and the achievement is simply a checklist of the chapters it contains. What decides whether you finish it is whether you did the side chains as well as the main thread.
Getting the zone at all
Two things have to happen before any of these chapters exist for you.
First, finish the Battle for Azeroth introduction. For the horde that is the chain around Welcome to Zandalar, and until it is done the zone map in Dazar'alor offers nothing.
Second, choose Vol'dun from the map in Dazar'alor. The three zones of your continent are picked one at a time, and a zone you have already selected has to be finished before you can switch to another.
This achievement is Horde only. There is no way to earn it on a character of the other faction, and it cannot be traded across an account by any route other than levelling a character on that side.
The 7 chapters
| Storyline |
|---|
| Unlikely Allies |
| Dangers in the Desert |
| The Warguard's Fate |
| A City of Secrets |
| The Three Keepers |
| Storming the Spire |
| Atul'Aman |
Vol'dun is the most linear of the six: the story is a single journey from the northern coast to the pyramid in the middle.
Atul'Aman comes after the rest and reads like an epilogue rather than a chapter, which makes it the one you can leave the zone without having seen.
The order matters less than the count
Chapters overlap: you can usually hold quests from two or three at once, and the game does not present them as separate stories. That is precisely why people finish the zone believing they are done.
Before you leave, open the achievement and read the list rather than trusting the feeling of having finished. The chapters that are missing are almost always the ones that never appeared on the critical path.