From a start door, climb a ladder on your right.
When you get to the top of a ladder, there is a wooden box on your right.
Swallow and drop it into the left-side hole next to a ladder.
After that, climb the ladder on the left edge.
There is a wooden box above the ladder and a key is inside the box.
Get a key by breaking a wooden box and remove two boxes on your right by swallowing.
Go toward the right, and there is a goal door surrounded by wooden and iron boxes.
Break solid wooden boxes by kicking five times, and break a fragile iron box by kicking ten times to enter a goal door.