The Warehouse is an area accessible from the Nail World, via the Red Nail Passage. To get into this area, you need to pass directly through the Window Room (going right-to-left). After exiting it, search for three bloody nails outside of the nail path. They will transport you to the Warehouse's outside area.
Features
Outside Area
The outside area contains some wooden statues, laid-down arches with black trash bags, rectangular arches, and the Warehouse, a very large building.  From the outside, is possible to see a rotating triangle on the rooftop of the Warehouse.
Inside Area
In the hall there are building projects. Entering the doors takes you to different rooms, some of them have lots of boxes, and some are blocked with wall glass. There are four floors in the warehouse that you can access through the stairways. At the top floor there is a white passage and you'll see again the rotating triangle. By interacting with it, you'll get the Polygon effect. Interestingly, if you use the Chainsaw on it, you'll hear a scream but there won't be any blood. Its sprite changes to a box-shaped thing briefly before fading away.  A white door is also found on the top floor, going through it takes you to a room with stairs. By going down the stairs and passing some rooms, you'll find a four-leaf-clover. Interacting with it transports you to Grass World.