The Gardens Between

There are 7 "worlds" in the game, each with 2 or 3 levels. Once you complete World 4's three levels and see the memory of the two kids playing video games and eating popcorn you "Can" get this Achievement.

I say "can" because you have to find it in the memory. While the memory plays you can move left or right to play the memory or rewind it. Keep playing through it until an object in the area shakes and makes a sound, once that happens freeze on that scene and a little box will appear and unlock the Achievement.

In order to get this one, you have to rewind until the poster on the wall starts to shake, then freeze the screen until the little box appears from behind the poster. Below is a video for reference.

The gardens between has a total of 8 worlds but only seven of them have achievements at the end. each world consist's of 2 or 3 missions once completed you will be taken to a screen where you see a set of star constellation this is where you can get your achievement.

for this achievement you need to lock on to the poster on the wall behind the boy once locked on to the poster it will start to shake give it a few seconds and your achievement should pop.

for the people who prefer video guides