Due to scheduling conflicts I am no longer able to update this guide. Instead, I invite everyone to go to the INFRA official Discord, where a dedicated team of problem-solvers are working together to solve this and other deeper mysteries, along with additional clues from the developers. The Discord is at:

https://discord.gg/SEnuPAE

I also recommend the Stalburg wiki, your one stop shop for INFRA Info:

https://stalburg.arctar.us/Main_Page

I'll touch base when I can. Thanks for keeping the hunt alive!

The initial trailhead for the INFRA Secret, and the first thing most players discovered, was a corpse hidden in a locked room near the tunnel entrance. The tarpaulin covering the corpse had a series of letter-number combintions on it:

The total encoded sequence reads:
B1 C3 F1 B2 F2 C4 E4 G3 B2 G1 F4 B4 B2 G1 G2

Current progress:
"I (C3) (F1) THE (F2) (C4) (E4) TELL THE RIGHT THREE WORDS TO THE RIGHT PERSON"

Looking for what this sequence says is one of the core goals of this secret hunt.

Most secret riddles in INFRA are associated with a letter-number pair, e.g. A1, B3, etc. These values range from A-G and from 1-4. In other words, we've found F2, but not X9. Each of these pairs has a puzzle associated with it, and the of that puzzle is one or more words. Sometimes the answer is plainly visible, sometimes the puzzle is frustratingly complex. So far, all of these puzzles are self-contained.

These three combinations are encoded in binary under labels that appear on a control panel model throughout the early areas of the game.





Right dial(A1): WHAT
Left dial: (A2) HAPPENED
Center dial(A3): TO
These control panels require additional scrutiny. The letter A does not appear in the corpse message, so something else may be going on here.

Found by AbueloNemesis.

The first control room in Stalberg Steel Factory has a control panel with duplicates of the first three A series dials. To the left is an additional pair of dials:

http://steamproxy.net/sharedfiles/filedetails/?id=655103861

In the first one there is a funny "Stop reading these!" easter egg. But the interesting one is below.

http://steamproxy.net/sharedfiles/filedetails/?id=655103767

N12 BA4 N
0100000101001000
Translates to "AH", presumably a reference to Alex Hartman. This means the full A-series so far is "WHAT HAPPENED TO AH"

We should however also look for additional A series labels, and keep an eye out for anything that would provide context or explanation for the N12 B and other N in that label.

B1 is I.



This is the train signalbox switch.

I am very proud that I solved this difficult conundrum.

B2 is THE
B4 is TO

Credit for discovery goes to Nius.
http://steamproxy.net/sharedfiles/filedetails/?id=642717867

Both of these terms are found on a generic control panel, first seen in the lower Hammer Valley dam. The panel is easiest to read in the Pumping station, where it appears without rust.

B3 is probably IN:

This is the override panel near the infamous generator G2.

This is the elevator fusebox at the top of Hammer Dam.

B3 is not used in the corpse message, so its significance isn't known, if any.

C1 = IS, on a fusebox at the top of the Hammer Valley Dam.

F4 is unknown, and so far hasn't been solved.

Graffiti on an information board at the bird lookout tells us that the solution of F4 is three words:



Beyond this, we're not sure. One possibility is we need to examine other information boards in the Hammer Valley area for words that are altered or otherwise distinct. Another possibility (person who told me this, give me your name so I can credit you) is that the answer is literally "3 WORDS".

G1, 2 and 3 were located on a board in the water treatment plant offices.


The first three rows appear to provide XY coordinates for the letters of individual words, but a number of wrinkles in how they are displayed made this hard to figure out. User tsl16b solved this riddle, although this board might come into play in the future...

Explanation:
[WIP]

Solution:
G1: RIGHT
G2: PERSON
G3: TELL

Multiple other messages not related to combinations or the corpse message have been found in out-of-the-way places ingame. So far, all of these have been in binary.


Location: Hammer Dam control room

The binary onscreen translates to:
Help me! I'm stuck in the south tunnel B2


Location: underside of residential area mailbox

The binary translates to:
The truth is in tunnels Robin

Robin is one of the known water tunnel maintenance workers, known for being crazy.

Images that may be important, but haven't been explained or translated will go here.

Left dials: NOTHING HERE OK
Other parts need to be checked, or may all be without meaning.