From a start door, climb the right-side ladder of a door.
After you climbed, go to the right and go up stairs made by wooden boxes at the right edge.
Swallow the top wooden box of them and arrange it to go up the upper left brick floor.
After you got to the upper floor, bring a box placed on your left to the middle of the floor and then go up the upper right floor.
Climb a ladder in front of you.
Go forward to the left and break the left-side wooden boxes.
Fall down from the left-side edge of the floor.
After that, break wooden boxes on your left and get a key.
Then enter a goal door placed on your right.