How do I get this achievement. It says "enter the void" but I can't figure it out.

Polo and Karts. Add an extra seat behind, and another player can move side to side to wield the polo stick on either side of the kart and hit the ball. If its played in SP mode the player could choose to be the driver or the polo player in backseat. The polo player can push other karts nearby away if the angle is right and close enough. Basic track editor, basic as large oval arena where you can define the track and change terrain height and place stuff that can be knocked over or solid props....