To get this achievement, you must have unlocked the Tower level.
Once you have, you will need to progress through the level until the point you reach an area that has a seemingly out of place radio and vehicle (Hover Junker) as well as the Hover Junkers level module.
Just below this area is a reclamation bin. You will need to grab the aforementioned module and place it into the reclamation bin below.
Once you have done that, go ahead and exit the Tower level and you should now have unlocked the Hover Junkers sandbox level as well as this achievement.