The Shed.

The shed is a small house in the game. But the door is blocked by a tree branch but Arthur and Buster find a saw when they are at the waterfall, as Arthur cuts the tree branch, Buster is near it and then the tree branch falls on him and then the door can be opened again. Then Arthur and Buster find a screwdriver on the floor and Arthur and Buster use it to fix the third step on the ladder to the fire tower.