I found it weird that no one has mapped this yet, but now I kind of see why. It is a bit boring, but still plays a part in bringing back memories.
This map uses a wall with negative width that covers the entire map, making it feel like underground.
I forgot that inside a wall you get permanent vibrations. I recommend to install the tweak55 from mod assistant in order to turn vibrations off when “touching” walls.
I removed the wall from standard diffs and made properly labeled diffs for it.