This is not a full walkthrough. If you get stuck I recommend trying to use the Imag (C key). Use a video walkthrough if you need more help.

You cannot replay chapters in this game, so don't rush. I earned 100% completion without using a guide, so it's not extremely hard to earn 100%. The game only takes 3-5 hours to beat, so you may want to use this guide on a second playthrough.

All images in this guide are taken from wypepsi's guide. I do not take credit for this work. Please leave him a thumbs up if you appreciate his work.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3023136328

Last Round!
Drink with Sara.
Collect the Illumium during Chapter 4 by using the Imag on Akos's corpse just after escaping from The Raven. Then visit Sara in the Mess hall during Chapter 6.

Resist!
Find all 3 'Resist' propaganda posters.


Poster 1 - Chapter 4 on Level 2 by the Nautilus model
Poster 2 - Chapter 6 in the Mess hall
Poster 3 - Chapter 6 in the Supplies/Treasure area

Jules Verne
Gather all Bios, Verne Logs, and Collectibles. See the other sections for details on this achievement.

Biographer
8 Biographies Found!

• Imag - Chapter 1 (unmissable)
  
• The Nation - Chapter 1 on a corpse in the Armory
  
• The Valkyrie - Chapter 2 near the Bridge
  
• Edrielle - Chapter 4 in Nemo's Office
  
• Captain Nemo - Chapter 4 in Nemo's Office
  
• The Echo Guard Chapter 4 (unmissable)
  
• Cedric Collingwood - Chapter 5 after collecting all 4 Algae
  (Algae 1) just after the giant clam
  (Algae 2) after descending into the temple, go left towards the rocket mural
  (Algae 3) by the fossil, go right before descending into the temple and use the Imag
  (Algae 4) inside the 2nd Trial door
  
  What a Fossil!
  Find the fossil during Chapter 5.
  
  
  Vaccine
  Gather all 4 Algae during Chapter 5.
  
  
  
• Phobos - Chapter 5 during the 4th Trial
  
• Plaseia - Chapter 5 (unmissable)
  
• Madeleine Turner - Chapter 6 after looking at all 3 'Resist' posters
  (Poster 1) Chapter 4 - Level 2 by the Nautilus model
  (Poster 2) Chapter 6 - Mess hall
  (Poster 3) Chapter 6 - Supplies/Treasure
  
  Resist!
  Find all 3 'Resist' propaganda posters.
  
  
  
• Suni Kyun - Chapter 6 (unmissable)
  
• Nadine - Chapter 7 near the start of the island
  
• The Ancestors - Chapter 7 (unmissable)
  
• Bloody Raven - Chapter 7 (unmissable)
  
• The Flame of Hephaestus - Chapter 7 (unmissable)

Memories of a Writer
5 Verne Logs Found!

• Five Weeks in a Ballon - Chapter 3 on the elephant on day 2
  
• Center of the Earth - Chapter 3 in a small tunnel to the left while descending the petroglyph cavern
  
• Robinson Crusoe - Chapter 3 at the bottom of the petroglyph door cavern by two red chairs
  
  
• Verne and Energy - Chapter 4 (unmissable)
  
• The Nautilus - Chapter 4 on the ship model on Level 2
  
  
• The Journey to the Moon - Chapter 5, after descending into the temple, go left and use the Imag to repair the wire. Then look at the rocket mural.
  
• Passion for Science - Chapter 5, by Algae 3 and the fossil, to the right of the temple
  
  
• Verne's Office - Chapter 7 after talking to Nemo, up the slope before the ladder
  
• Pierre-Jules Hetzel - Chapter 7 after talking to Plaseia (unmissable?)
  
• Verne and Volcanos - Chapter 7 inside the cave, to the left after going down the first ladder

Collector
5 Collectibles Found!


Deep Knowledge
8 Collectibles Found!

• Letter I - Chapter 3 near the start of the island
  
• Letter II - Chapter 3 to the right of the lift
  
• Letter III - Chapter 3 by the mural with two snakes
  
  
• The Volcano - Chapter 4 in the Infirmary
  
• The Island - Chapter 4 on Level 3 while stabilizing the Blue Blood
  
• The Cave - Chapter 4 after escaping from The Raven near the crane
  
  
• Primordials I - Chapter 5 after descending into the temple, to the right
  
• Primordials II - Chapter 5 by the lava
  
• Primordials III - Chapter 5 to the very right side of the area of the 4 door trials
  
  The Nautilus
  Gather Nautilus I, II, III.
  
  
  
• Nautilus I - Chapter 6 in the Library to the left of the organ
  
• Nautilus II - Chapter 6 in the Bunks area
  
• Nautilus III - Chapter 6 in the Treasure/Supplies area
  
  The Mysterious Island
  Gather Ancestors I, II, III.
  
  
  
• Ancestors I - Chapter 7 in the cave just past the entrance
  
• Ancestors II - Chapter 7 in the cave. Go down the first ladder, then right, then up the next ladder.
  
• Ancestors III - Chapter 7 in the cave. Go down the first ladder, then left and down the second ladder.

The Siege of the Nautilus
Complete Chapter 1


The Mnemeogram
Complete Chapter 2


The Annabel Lee Castaway
Complete Chapter 3


The Truth
Complete Chapter 4


Kraken
Complete Chapter 5


Sabotage!
Complete Chapter 6


The Archenemy Defeated!
Defeat Bloody Raven


Journey to the Center of Hemera
Complete Chapter 7


Power of Imagination!
Complete the game.