This is a Hexen mod I made that runs on the source port GZDoom. It contains non-Euclidean geometry - sometimes, when you look behind you, the room is different to the one you were just in! I've also modified one of the monsters to better predict the player's movement patterns so that they can lead their shots. For more information see the enclosed Twisted_Reality.txt file.
To edit and view the WAD file, I use Slade which is free. Slade download link: https://slade.mancubus.net/index.php?page=downloads
To play the WAD you need the free source port GZDoom and the not-so-free Hexen IWAD which you can buy on Steam. Fortunately, ShadesMan has made a video of themself playing my map which you can watch on YouTube: https://www.youtube.com/watch?v=No_eOpvK2_E&t=1767s
I released this project on Doomworld (among other places): https://www.doomworld.com/forum/topic/123133-twisted-reality-hexen-gzdoom-only/