In the level Carry there are four sections, each with a box used to open the door to the subsequent section. For this achievement you must stack all four of these boxes. You can use a second controller if you have one to stand on the pressure plates to quickly drag the boxes to the next section. If you don’t have a second controller, this is still easily done.
Place the first box on the pressure plate to open the door. Head through into the next section and bring this box back to the first section. Replace the first box with this box, then bring the first box through the door to the second section.
Place this box on the plate here. Go back to the first section, grab the box there and jump off the edge with it. You’ll then respawn in the second section and now have two boxes with you. Now you just have to do what you did with this box for the box in the third section.
Take the box not on the plate to the next section. Drop it down and push it up against the higher ground you just dropped it from. Grab the third box, place it atop this box, then take it to the second section. Replace it with the box on the plate and take that box to the third section.
Now jump off with the box in the second section to respawn with all three. Use the lift to place a box on the next pressure plate, opening the door to the fourth section. Take this final box back to the third section via the lift and boxcar.
Stack two of the boxes up against the higher ground by the lift. Take the other two up the lift and stack them on the two below and the achievement will unlock.