Anyone played the Trailer in the game?

[Kein]

Rather interesting, looks like it was earlier Prison.

Hmm... it says (@ the beginning) that it's unaltered gameplay, so, I wonder, why devs totally redid the whole location.

It is still actual, unedited gameplay, just in a level that does not exist.

Maybe it exists in the game files but is unused and would require some console\custom story haxing (so to speak) to open?

Amnesia's resources is open for everyone. There is NO such maps.