It’s vanilla HL2, but mirrored.
Really simple concept, but a complete mind-twister; feels strange to get lost in maps one has played for close to 20 years and your motor memory completely disagrees with what you’re seeing.
Get it here:
And here’s how I did Highway 17 in this mod:
It’s also done in a sadistically clever way: your vision is mirrored, your controls are also mirrored, and then the cherry on top is that even the textures are mirrored so that they will appear normal when mirrored - yeah, I know