Forza in the Fall Achievement in Halo: The Master Chief Collection

This achievement can be earned on the Easy difficulty (or higher) on ONI: Sword Base.

After clearing our the initial courtyard firefight and passing through the bunker-like structure into the next area of the mission, there are two hidden switches that, when activated simultaneously, will unlock a racetrack-like Easter Egg. Because there are two switches, and they must be activated at the same time, this achievement will require either a second controller or another player.

Please refer to the video guide below, courtesy of Halo Completionist, for more information regarding the location of the switches.