Introduced with the Heavensward expansion for Final Fantasy XIV, up to 24 players can take part in this raid.
Once you've unlocked two Alliance Raids they'll be available in the daily Alliance Raid Roulette, along with any others you might unlock later.
Unlocking Dun Scaith FFXIV
In order to unlock the Alliance Raid, you will need to complete the quest called Where Shadows Reign. This quest is available by talking to Stacia in The Sea of Clouds (X: 6 Y: 5).
If you cant see the quest, here is how to get it!
To unlock the Where Shadows Reign quest you will need to finish a few other quests.
This quest is given by Leofard in The Parrock (X: 7 Y: 6)
This quest is given by Stacia in Sea of Clouds (X: 6.2 Y: 5.8)
This quest is given by Utata in The Sea of Clouds (X: 25 Y: 5)
You're good to go!
You're now able to access the Dun Scaith Alliance Raid.
If you are looking to upgrade your relic after Patch 5.35 of FFXIV here is the quickest way to farm the sixty Memory of the Dying
With Patch 5.45 the new Relic Weapons upgrades are now available in Final Fantasy XIV. Here's how to get the Loathsome Memories of the Dying and upgrade your Resistance Weapons.
Should probably add "Sky Pirates" to that list of quests you must complete first as it's the initiating quest in the chain. Available after Heavenward MSQ is complete in The Pillars right outside of House Fortempt.