This guide will eventually help you get 100% of the achievements. There are spoilers bellow, so i'd suggest at least completing the game once before reading it.
How to Obtain All Achievements / Trophies
- Awoke with fragmentary memories after the crash of the Cassandra.
- Followed Salim's trail.
- Dreamed of Paris.
- Carried on with life, despite Salim's fate.
- Followed the pilgrim's trail to take refuge in the fort.
- Explored the inner fortress, and spoke to the doctor.
- Took time to talk with an unborn child.
- Fired a cannon at the fortress gate.
- Found a way through the ruined cistern.
- Travelled through the desert.
- Took a walk in the park.
- Escaped the Shadow.
- Escaped the Shadow.
- Activated the alchemists' device.
- Drained the fear and the life from a crewmember.
- Activated a portal between worlds.
- Operated a scanning device, and learned of a child's illness.
- Failed to reach a child, separated by deep waters.
- Reached the doctor.
- Gave birth to a daughter, only to lose her.
- Completed the Story.
- Sent extra objects through the portal in the Alchemist's Chambers.
- You're required to send a specified number of objects (I guess between 6-9) through the teleporter in the lab located in the other dimension. Behind the teleporter is a shelf with more than enough stone cubes to choose from.
- Resisted fear, and resisted anger.
- Escaped a cage in the Arsenal without setting off a grenade.
- While fetching the sulfur solution for the tank shell composition. Enter the cage by jumping across the scaffolding outside the window next to the cage, this lets you enter the cage without triggering the grenade. Get all relevant items in the cage and fetch the key from the guard leaning against the cagebars (holding it in his hand). (Carefully) remove the hook from the door and unlock the door with the key.
- Smashed lots of irreplaceable objects.
- Smash a set amount of vases. I would guess it can be as many as 20.
- Tortured an innocent to aid an unborn child.
- Create the vitae as shows in the video and then use it in the chair.
- Spared an innocent, perhaps dooming an unborn child.
- Power up the cart and leave without creating the vitae.
- Kept quiet and still, and so escaped a predator's gaze.
- Go prone (hold CTRL with standard keybinding) near an enemy without being detected. The best places to do this, is either in the factory just after you pick up the power triangle, or in the lower factory after you fall off the cart.
- Left when things were getting interesting in Amnesia: Rebirth.
- As you enter the caves. After reading Salim's letter and walking a short bit into the dark hallway behind it, you can save and exit the game to quit to unlock this achievement.
- Completed the game faster than any Frictional developer.
- Collected all the other achievements.
For these achievements you can do them one after another by clicking continue when going back to the main menu after finishing the story.
- Escaped to Paris with a daughter that must now be cared for:
- Once you've soothed Amari after picking her up from the crib, take the Leyden Jar before exiting the room. When the boss fight starts, Go to the door use entered from, using the structures to avoid her gaze. Then use the Leyden Jar to power the portal
- Left a daughter in the care of a god, and was reborn.
- Once the boss fight starts, put Amari back in the nursery.
- Sacrificed everything to cast down a god and end suffering:
- Once you've soothed your baby after picking her up from the crib, take the Leyden Jar before exiting the room. When the boss fight starts, go to each of the rooms around the side, starting with the first on the left (whilst avoiding the spirits gaze). Use the Leyden Jar to open the doors and then inject the valve.
- Found an unfinished letter from an archaeologist to his sister.
- The historian achievement is triggered in the Fort. While searching for a way to the radio in the house, on the same floor (2nd) as the cannon which is needed to break the floor are some stairs leading up to a well lit corridor. Going up the stairs and taking a left at a junction, you will traverse another flight of stairs and see a covered box. In said box is an unfinished letter. Reading it unlocks the achievement.
- Found treasure beneath the water.
- Located at the desert oasis right after traversing a riverbed in the desert. In the middle of the oasis is a rock. Underwater and near that rock is some old pottery. Hidden in that pottery is a can of oil which triggers the achievement.
- Collected notes to fill a journal.
- Burned a forest's worth of matches to illuminate dark places.
- Gazed at a reflection in the water.
- Found all Hank's notes on the crew of the Cassandra. How to complete it see this guide.
- Found all the memories recorded by others. See this guide how to complete.