The bsp takes a little getting your head around but its a real impressive design. I found a few vids on quake but the collison detection is way over my head
I wasn't impressed, it felt like the same old stuff just in VR I got bored after an hour and never touched it again. Alien Isolation VR did blow me away, the detail and atmosphere is awesome, I was actually afraid while moving around and when I met the alien I felt real fear running away
https://www.youtube.com/@MattsRamblings
PVS from the top
https://www.youtube.com/watch?v=TMeUxF4mHJA
You might find this code helpful.
https://www.codeproject.com/Articles/32751/Half-Life-Game-Level-Viewer
https://blogs.unity3d.com/2019/03/13/2d-pixel-perfect-how-to-set-up-your-unity-project-for-retro-8-bits-games/