Here is the full list of all 30 Avadon: The Black Fortress achievements.
Fight your way back into the castle.
Get your main character to level 30.
In the Farlands, no foe of the Pact can be left standing.
Bring all four of your allies back to Avadon.
Cleansed the Beraza Woods of bandits.
Augment ten items.
Eliminate the threat to the Kva.
Purged a tower of its unspeakable experiments.
Get your main character to level 20.
Show that Holklandans and the Kellem can work together.
Locate the crypt of the Keepers.
Showed the ogres just how foolish they were.
Hunted down the Shadow Beast.
Get your main character to level 10.
Calm the dragon Zhethron. For the first time.
Meet Redbeard.
Found a secret door.
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 Normal difficulty or higher.
Complete Avadon: The Black Fortress on Hard difficulty or higher.
Complete Avadon: The Black Fortress on Torment difficulty.
Prove your loyalty to Redbeard.
Claim Avadon for your own. (Normal difficulty or higher.)
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.)
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.)