This achievement can be found in the 8th level of the game "Modern Art".
At the beginning of the level turn left and go through the double doors, this will take you into a room full of cassette tapes. Run past these and take your first left into a large room with a zebra rug. In the back right of this room is a door to the security room.
Inside the security room, there are six monitors above the computer. Please take note of the colours on the screens and their position. Turn around out of the room the way you came, but turn left after the room with the zebra rug. Go out the double doors and turn left up the stairs then take a right and jump off the balcony.
This will put you in front of the TVs you must enter the code you got above. Once done correctly the door to your right will open and the Katana is on a stand at the end. Pick it up and destroy the mannequins in the room. Your achievement will pop.
*You can also see the code on the mirror attached to the ceiling in the glass maze room (but it does not always work)*
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