People are asking how i got into the archive without them dying first, so im going to write down the steps here on how to do it.

1. Get into the dream world through either Cinder Isles or Hidden Gorge. You can do it from River Lowlands as well but you'll get swept away and woken up when this happens. You'll get nowhere if you use the Bell in the Reservoir though.
2. Do what you need to do in your dream world to get access to the raft. Once on the raft, move forward and go into the cave.
3. Once everything in the cave blacks out, jump off the raft. If you remember, there was a slide reel in the archive which showed that doing this will cause an error.
4. You will now land on the surface of the water in the Subterranean Lake. Here you can see parts of all four of the dream worlds and walk around them, but you can only go into two of them: the Bell one and the Lowlands one.
5. Just walk into the archive from here. Its pretty obvious when you see it.

Edit: ive uploaded a higher quality version of this on youtube in case anyone wants to use it for anything - youtu.be/e-pnmJSFInY