The Sourceruns team have completed a 8:31.93 run of Portal, which is absolutely ridiculous, brilliantly devious and laudably investigative. The latter descriptor is appropriate because of the level of understanding required to complete the run. These glitch-hunters have an in depth knowledge of each chamber, of the Source engine and of the strange ways in which portals work. You can watch the run below, and read about the techniques used and the analysis of each chamber in an extensive document. Oddly, the closest I think I've ever come to exploring a game in this way was when I played deathmatch Doom for an entire year without stopping. I knew every layout and every trick, and I was still rubbish.
...to be SDA legal we have done our run without using AutoHotKey scripts for any portion of the run. This run first started after the discovery of a new glitch, which snowballed into a whirlwind of discoveries of new tricks, skips, and glitches. We started running chambers in April, took a brief hiatus, and then resumed work in late June. The bulk of the run was completed in about 2 weeks time.
With a break to make a coffee just after embedding that video, it's taken me longer to write this post than it took for these guys to complete Portal. Sort of. They've put almost 850 hours into the game between them and I'm guessing at least some of that was spent perfecting each chamber rather than just enjoying GLaDOS for the umpteenth time.
This is about as far away from the way I play games as it's possible to get without digitally downloading them to a box of tissues, but I'm fascinated by the glitches and the things meant to be unseen, as well as the breaking point of an engine, a mechanic or even an entire world. Speed runs, at their most speedy, tend to exploit those things, existing at the limits of what the architecture of a game has achieved, and I salute them for that as much as the actual timed achievement.
In case you missed the link above, here's the lowdown on how each chamber was completed.