So I am a digital hoarder, and going through everything I've ever downloaded and saved from the forums and such, I came across a file called Paradox.cd. Upon opening it, this is what I'm greeted with, and I'm curios if anyone knows who created it? I'm genuinely interested in how this was written. The room you start in is a small room, the back wall (closest blue wall) is actually a full wall, but if you walk through the corridor shown, you go through a "portal" into the next room that you can see there. The screenshot doesn't do it justice honestly.
[img]https://ibb.co/DztNV15[/img]

I have been experimenting with similar ideas in my game Paradox Vector, but this is not my work. I used cleverly placed teleporters to move the character seamlessly between similar looking areas, so the illusion of impossible geometry is perceived.

https://www.youtube.com/watch?v=TdCUr4b6JaA

It looks in this case that they may have used a VIEW portal of some sort, so the hallway is projecting a view of that room on a passable screen. I have not attempted this approach myself, but it seems like a likely way to try something like this.

i have no idea