Highly recommend everyone that likes Portal to try speedrunning it. It's pretty short, especially if you have practiced chamber 16/17/18. You can beat the whole game in 1-2 hours, but it will go down to more like 40 minutes without glitches if you have the solutions memorized.

Then you can save like 15-20 more minutes by learning a few really easy glitches. There's tons of tutorials on speedrun.com/portal, too