The Storm Quelled

For reaching the secret ending, where the achievement will unlock after the credits.

To get the secret ending you must have completed "Regrets of the Dread Wolf" peacefully (see Clear Minds and Open Hearts).

You also need to collect three Mysterious Circles:

One is on a tiny island in Arlathan Forest, solve a laser/crystal puzzle to get to the island.

Another is in Necropolis Halls after The Unbound - its on the left side in the room where you had the big battle.

The last is in Crossroads, complete the quest "Heart of Corruption" to get access and the circle will be on the left where you climb up in the room where you fight the dragon.

Then, go ahead and complete (or re-complete) the game for the secret ending and cutscenes.