There is a secret area in the section right before you encounter big red. More percisely, the north ladder area of 4th area of the abandon factory. You need thw chainsaw to gain access by breaking one of the sewer grates in the area. I think it is the third one that you encounter from the where you start in this area. The secret area itself features a house across a moat with a tea kettle sitting near the door entrance. there is a bridge to the house but, it has cone impeding you path. beyond the moat the a bunch of flowers similar to the ones in abandon china town and there is a gray cube that takes you back to where you came.