This is level 8 of the Way Back. If you clicked on this level on the Galaxy Map, after the cutscene "Boat Ride", you were skipped into part 9. When you beat that, press the "previous" button and you can play this level!
Note: Parts 8-16 of this tunnel can only be played with the Duplicator, so he will be the only recommended character.
There are a couple of different ways you could attempt this level. The best way to beat this level is to jump off the angled boxes. If you feel uncomfortable with that (though you must already know how the boxes work as you had to beat the Box Storage Area to be playing this level), you can try to follow the snaking platforms instead.
- The Child's balloon fell out of the boat in the cutscene "Boat Ride", and it can be seen here.