Cocoa Puffs once featured this "maze" or "obstacle course" that was permanently attached to the back of their box. The design was in a canyon like setting. To assemble this contraption, you had to tear a part of the attachment and that allowed you to then pull it out so it was 3D like (like assembling a mailing box). NOW what you would do is pour the cocoa puffs at the top of the course and they would roll down to the bottom going all over the place and eventually end at the bottom where you placed your bowl. Sometimes the cereal would get stuck at corners and there were tabs that you had to flick to get them out.

does anyone have a picture of this? I tried googling it but no go. This was probably one of the coolest 90's "toys" and it was not even an actual toy!

I'm not sure if this is what you're asking about but from 1991 here is a pull out game from the back of a Cocoa Puffs box.

Here is the caption:
"This is an empty flattened 13.75 oz box of Cocoa Puffs cereal from 1991. On the back it has a Help Sonny find his bowl game".