Of the twenty-seven achievements that come packed with Close to the Sun, eleven are tied to finding all the collectibles within the ten chapters of the game. This guide documents the said collectibles (63 in total) in order of chapter / gameplay progress. Albeit not related to the collectibles themselves, three missable achievements are also mentioned within their respective chapters.

Since the game itself does not offer a gamma slider, all screenshots contained within are slightly tweaked out of game for better clarity.

There are 5 passports and a tube message to collect in this chapter.
1:3 - Nicolas' Passport
On the seats to the right upon entering Hermes.
Tube Message 1/8
On the platform to the back of the offices.
1:2 - David's Passport
At the upper floor of the offices.
1:1 - Silvia's Passport
On a desk in the interrogation room.
1:5 - Jung-hwan's Passport
On a desk in the map room.
1:4 - Ananya's Passport
In the security booth reachable from the map room.

There are 5 masks to collect in this chapter.
Upon starting the chapter, go up the stairs and use the bell on the reception desk ten times to unlock the 'Lousy Service' and 'Demanding Customer' achievements.
2:5 - Mask: Weather Tech
On a desk to the left of the piano in the main hall.
2:1 - Mask: Bio Labs
Near the base of the central statue in the main hall.
2:3 - Mask: Dim. Physics
To the right of the stairs descending to the main hall.
2:4 - Mask: Tech Labs
To the right of the security booth in the main hall.
2:2 - Mask: Ship Security
On top of the bar across the security booth in the main hall.

There are 5 photos, 3 keycards and a tube message to collect in this chapter.
Tube Message 2/8
At the bottom of the stairs descending to the first floor.
3:5 - Photo of a Married Couple
In the fountain near the gym on the first floor.
3:8 - W. Steinitz Keycard
On top of a chessboard near the stairs to the second floor.
3:4 - Photo of Someone's Wife
On the bed in the guest room titled 'Fire' to the back of Epsilon quarter. The key to the room must be collected from the reception.
Entering the guest room in question unlocks the 'Happy Birthday' achievement.
3:3 - Prosper Family Photo
On a corpse found upon climbing up the ladder near the rail station.
3:7 - A. King Keycard
On the bar at the entrance to Gamma quarter.
3:2 - Miller Family Photo
On a coffee table at the entrance to Alpha quarter.
3:1 - Brown Family Photo
On a nightstand in C.F. Brown's room, which is unlocked after the dialogue with Tesla.
3:5 - L.J. Ostrog Keycard
In the safe of C.F. Brown. A puzzle must be solved to access the safe in question.

There are 8 blueprints and a tube message to collect in this chapter.
Tube Message 3/8
In the labs' reception area.
4:1 - Blueprint: Death Ray
On a desk in room 210.
4:2 - Blueprint: X-Ray Machine
Near a corpse in room 214.
4:3 - Blueprint: Earthquake Machine
On a filing cabinet in room 323.
4:5 - Blueprint: Lightning Harvesting Machine
On the large desk in the lecture hall.
4:6 - Blueprint: Ball Lightning Machine
On a table in the room littered with dissected rats.
4:4 - Blueprint: Artificial Photosynthesis Inductor
Near a corpse in the laboratory with a red patient chair in the middle.
4:7 - Blueprint: Helicopterplane Machine
Next to her corpse in the office of D. Harnesk.
4:8 - Blueprint: Kinetic Rain Device
On a seat to the back of the waiting area of the labs.

There are 4 memos to collect in this chapter.
5:1 - Helios Physics Department - Expanding into New Sectors
On the desk in the side room accessible from the lobby.
5:3 - Helios Physics Department - Weather Department Incident
Near the pneumatic tubes on the second floor.
5:2 - Helios Physics Department - Core Memo
On the table at the back of the lecture hall.
5:4 - Helios Physics Department - Core Construction
On the reception desk after traversing the halls on fire.

There are 5 flyers and a tube message to collect in this chapter.
Tube Message 4/8
To the left in the lobby.
6:4 - Signed Opera Flyer
On a seat to the right on the second floor balcony.
6:2 - Signed L. Petronoca Flyer
On a coffee table to the right after the stairs leading to private balconies.
6:3 - Signed Steinitz Flyer
On the floor to the left after crossing the beam to the next balcony.
6:1 - Signed F. Fabrier Flyer
On the pianist seat in front of the stage.
6:5 - Signed Clown Flyer
On a wooden barrel after the chase sequence. Take the 'Slow' path.

There are 4 reports and a tube message to collect in this chapter.
7:1 - Maintenance Report #2318
On a pillar to the left reachable by extending the bridge in the engine halls.
Tube Message 5/8
To the right in the section with the pressure valves puzzle.
7:2 - Maintenance Report #2411
Next to a hydraulic pressure valve.
7:3 - Maintenance Report #2412
On a control panel in the Tesla tower observation deck.
7:4 - Maintenance Report Division Memo
Hidden behind a corner of the control center.

There are 5 sketches and a tube message to collect in this chapter.
8:1 - Sketch: Lung Augmentation
Behind some dividing curtains in Surgery B.
8:2 - Sketch: Specialized Fertilizer
Lying next to a console on the way to the reception area.
Tube Message 6/8
Next to the reception area.
8:3 - Sketch: Mechanical Implants for Muscles
On a shelf in the first floor of the garden.
8:4 - Sketch: Brain Waves Improvements
To the right of the generator on the second floor of the garden.
8:5 - Sketch: Bos Taurus Augmentation
Lying in a side corridor of the energy stricken halls.

There are 6 blueprints and a tube message to collect in this chapter.
9:1 - Blueprint: Tesla Generator
On an open container next to the tower entrance.
9:2 - Blueprint: Tesla Tower
On a table near a door in the halls.
9:3 - Blueprint: Tesla Tower
On a workbench found after climbing down the ladder.
9:4 - Blueprint: Tesla Tower
On a table in the energy stricken hallway.
Tube Message 7/8
Next to an interactable door after the chase sequence.
9:5 - Blueprint: Tesla Tower Station
Next to the pneumatic delivery system.
9:6 - Blueprint: Tesla Tower Station
On the desk next door after collecting the previous item.

There are 5 notes and a tube message to collect in this chapter.
10:1 - Personal Note: Paradox
On a workbench to the left after exiting the elevator.
Tube Message 8/8
In the harvest chamber.
Collecting all the tube messages unlocks the 'Letters from the Future' achievement.
10:2 - Personal Note: The Rift
On a desk behind the pneumatic delivery system.
10:3 - Personal Note: Time Travel
On a board in the harvest chamber.
10:4 - Personal Note: What's Wrong?
On the bed found on the second floor of Tesla's quarters.
10:5 - Personal Note: Eureka!
On a shelf behind the elevator in the pod chamber.