1. Set your graphics to the highest possible settings and turn all effects on.
       
2. Continue the game as normal, till you can see the code for the presure plate puzzle.
       
3. From there you need to run back as fast as possible to the next puzzle. Through the fast approach on the highest settings the maps ground should not be able to load fast enough, giving you a gap to fall though the ground

After falling into the void and respawning in the main room, the achievement should be unlocked on your account.