To get this achievement, you must first obtain the black light.
In order to get the black light:
Press the red button twice and a panel with roman numerals should appear.
Enter I III II II III I on the panel. A 4 button panel and a large lever should appear.
Pull the lever to the left.
The black light will be under the BENDER panel.
Now take the black light and shine it directly left of the BENDER panel at the leftmost edge of the screen. You should see a ghost outline and you will get the achievement.
Credit goes to Drea Warrior Princess who made this guide which I used to get the achievement myself (and has images if my explanation wasn't good enough):
https://steamcommunity.com/sharedfiles/filedetails/?id=46348...