Sorry for replying some more, I still can't find it following the right path (The right door and exploring all the doors from that path.)
All the chests didn't provide me with a key that works. Could you perhaps indicate me the room where the key is located in? I'm not sure which area I missed it in and since everything is already completed. It's hard to look around for.
The image shows how far I made it. I'm all the way there, even beat the Trench Worm a few times.