A few minutes into the game, after the tutorial-like introduction to the game's mechanics, you'll come to a large room with a blocky blue tree with blue cubes hanging (like fruit). Take one of these cubes (
) and put it into the box on the floor. Doing so will open illuminate the blue line on the floor and open a door. Step outside, walk to the edge of the ledge, and jump off. You'll be able to return where you started, and the achievement should pop just before you land.