Here is the full list of all 30 Avadon: The Black Fortress achievements.
Complete Avadon: The Black Fortress on Normal difficulty or higher.
Prove your loyalty to Redbeard.
Reach the endgame without ever using a Resurrection scroll. (Normal difficulty or higher.)
Reach the endgame without ever making one of your companions happy. (Normal difficulty or higher.)
Fight your way back into the castle.
In the Farlands, no foe of the Pact can be left standing.
Get your main character to level 30.
Cleansed the Beraza Woods of bandits.
Eliminate the threat to the Kva.
Purged a tower of its unspeakable experiments.
Show that Holklandans and the Kellem can work together.
Get your main character to level 20.
Showed the ogres just how foolish they were.
Augment ten items.
Hunted down the Shadow Beast.
Calm the dragon Zhethron. For the first time.
Get your main character to level 10.
Found a secret door.
Meet Redbeard.
Bring all four of your allies back to Avadon.
Hunt down the greatest prey. (Normal difficulty or higher.)
Send Beloch the Scourge back where it came from. (Hard difficulty or higher.)
Complete Avadon: The Black Fortress on Hard difficulty or higher.
Complete Avadon: The Black Fortress on Torment difficulty.
Claim Avadon for your own. (Normal difficulty or higher.)
Locate the crypt of the Keepers.
Reach Castle Vebeaux without one of your characters ever going unconscious. (Hard difficulty or higher.)
Augment 50 items.
Find all codex entries.
Reach the endgame and never have more than one character beside yourself in your party. (Normal difficulty or higher.)