Spoilers below. This starts in the market square during Chapter one. Side with the suspicious priest Ramien and against the inquisitor Hurlun. If you reveal the light of heaven twice, you can avoid killing him.
Go to the temple of Desna in the northwest of the Market Square. You may see a green vision here. Talk to Ramien and his fellow priest, Ilkes. Looking up at the temple head left to meet a servant of Arendae. Go to the house he reveals. After saving the guests, talk to the bard on the stage. Ask her about Thrall. She gives you an item, but don't worry about it. Return to Market Square. Immediately forward and left is Thrall, disguised as a soldier. Do not let Hurlun take or kill Thrall. Good options can keep them both alive.
Return to the temple of Desna, and talk to Ilkes. Enter the temple and sing with the priests to unlock Azata path.
Proceed until the Lost Chapel in Chapter 2. After getting your second mythic level, enter the graveyard. On the right, there's a break in the wall. Follow the path, and make some athletic checks to get down. Down here will be a shrine with a map in it. Leave it there. Continue counterclockwise. A dead body near some Succubi has a small sextant. Take it and continue. You'll come to a cave. Inside the cave, there is a chest with a small harp.
Return to the shrine. Put the map, harp, and sextant in the shrine. Three hands will appear. Press them in this order: Middle, Right, Left, Middle. Choose the conversation option "Your voice seems familiar." You should get the achievement at the end of the conversation.