The Super_Secret file is a .rar file located in the redist folder of Amnesia, and is locked with a password only obtainable by getting all three endings of Amnesia: The Dark Descent. After every ending, you will get a part of the password, and you must combine the letters and numbers in order to get the password.
The password is lke271tyr299odn314.
The .rar contains four folders, each containing unique content regarding the developement of Amnesia: The Dark Descent:
- "Art" folder. This folder holds early concept art and similar stuff.
- "Creatures & Characters" folder. This contains early concept art regarding Agrippa, Alexander, and the gatherers (1-13).
- "Environments" folder. This contains art regarding the many different areas and objects in Brennenburg Castle (14-32).
- "Misc" folder. This contains a few paintings and drawings from around the castle (33-36).
- "Design" folder. This contains early game overviews and outlines.
- "Herbert's Lost Diary" Text file and sound recordings from a diary removed from the game. 
- One powerpoint presentation, and one .pdf detailing initial pre-alpha planning and overview from when the game was still known as Unknown.
- One word document containing maps, plans and descriptions of locations in the castle.
- Two JPEGs, one containing the outlines and planning from the Prison to the Orb Chamber, and one detailing the original layout of the Archives (37-38).
- "Engine" folder. This contains information regarding the HPL engine.
- Three sketches of the editor (39-41).
- A word document detailing the initial idea and design regarding the engine.
- "Video" folder. This contains video footage from early versions of the game.
- The password - lke271tyr299odn314 - Is a possible reference to some of the old nordic Gods - Loki (sometimes spelled 'Loke'), Tyr and Odin.
- 271, 299 and 314 are possible references to the mathematical constants e (Euler's Number), c (speed of light) and π (pi).