Originally, portal is one of the well known games to speedrun.
Goodigo, a friend of mine who streams his runs on twitch.tv, had an idea to reverse all the maps in the game Portal.
And that's exactly what I did.
I had problems with Chamber 15 but with the help of Avetixz (a very nice guy) I managed to fix it so it can be played in the final game. (Huge shoutout btw)
Playing this "mod" requires no glitch knowledge what so ever, however, I recommend playing the original game first and understand the basic mechanics of Portal (e.g. Flings).
This mod was created in under a week or so and I learned a lot about debugging and had a lot of fun doing this!
Submit your runs at speedruns.com and see how well you played the game through!