I admit it. Out of the entire mod, this seems to be the most difficult and least enjoyed portion of it. Two weeks after release, I began to work on an "update" to fix this. To fix 29, I'd have to do something I'd done several times before. Chamber 22 - Advanced is roughly the original version of Chamber 22. Chamber 26 - Advanced was the original vision for Chamber 26 that was abandoned shortly after beginning. 29, in its current state, will become Chamber 29 - Advanced, and the original chamber will be modified to be somewhat playable.
The key concept to understand from this is what I call the fifth fling. Two portals are placed facing up on two adjacent surfaces of unequal height. The player must repeatedly move from the higher to the lower in midair, gaining a bit of momentum each time. Along with the infinite fling featured in Chamber 19, it is one of the fling maneuvers that have been used frequently in Portal mods and map packs despite not appearing in Portal. It's also the hardest of them to pull off, and the game doesn't cooperate. While the infinite fling has found a good home in Portal 2's cooperative mode, the fifth fling seems to be dead in the water for now.
But what really went wrong in this mod? I seem to have failed to introduce the concept properly. Most everything else I've tried to introduce with as sterile an environment as possible, or even go so far as to have the puzzle solve itself the first time, usually with explosive results. Add the uncooperative nature of the portal funnel to the repeated nature of this technique and you've got very little room for error.
DAY 1: Attempt to salvage the game mechanic
I see if I can make this fling easier by giving more room for error. The simplest way to do this is to add height between the two platforms and reduce the number of repetitions required for success. The easiest way I could think of to do this was to add a glass platform to automatically rise up when stood on. I copied this piece directly from 22 (Android Hell). At this time, I also decide to use more distinct signage. In the Valve Developer Wiki, it was mentioned that when designing a level, you can't throw an arrow on the wall stating "GO THIS WAY. THIS IS THE WAY YOU'RE SUPPOSED TO GO. LOOK OVER HERE. OVER HEEEEEEEEEEEEEEEEERE!!" The fact that the test chamber environment is explicitly designed for the purpose that you, the player, are fulfilling when playing through the level opens the door to this and other techniques that would be considered a bit cheesy and unrealistic in other games. This is one of the main reasons I stuck through developing a Portal mod as opposed to the other games I tried playing around with.
Simultaneously, I decide to quite literally lower the bar and add a nice place to stand. If there's anything I've learned from all this, it's that people don't like shooting portals while flying. This doesn't work as well as I hoped it would. This fling needs to happen in a simple room with very simple and specific places to put portals. Unfortunately, 29 has a "hub" layout, in which a particular room will be visited over and over. This may need to go, and the level may need to be reworked into something a bit more linear. Most players can probably solve 29 perfectly fine as long as they aren't tossed in all at once. I later delete most of the observation rooms and decals, going back to a fullbright shell.
DAY 2: Toss it
Learning this technique is unneccesary, as no other chamber uses it. I find that this chamber could be easily replaced with three of the other four flings. This still means a total overhaul of the chamber. The basic layout is complete, though a few puzzle components are no longer in working order. The central "hub" room has been split into a lower double/vertical fling challenge and an upper "hub". The "goo room" has been rearranged to be used with the vertical fling (from the end of Portal's Chamber 18), and a small infinite fling challenge has been added to the front. The glass challenge has been rearranged a bit, and the approach to the "tube room" is now in a different place. The fifth fling challenge in that room is now a somewhat timed vertical fling with a raising platform that will kill the player for standing around for too long.
DAY 3: Basic lighting, decals
Fullbright hurts to look at. I do not enjoy testing levels with it on. It's time to add basic lighting. I copy+paste a few observation rooms back in that I removed before and make a couple of those metal block light things. It's far from perfect, but it's at least better than fullbright. In fact, at this time most of the new hallways and rooms are almost pitch black. I've added a few decals and signs as well. What I've most notably NOT added yet are the blue and yellow light strips that connect catchers/buttons to doors. These are very difficult to change once laid out, so they tend to go in last, along with portal bumpers.
DAY 4: More lighting, tests, planning
A few more tweaks to the lighting put it in roughly its final state. A new room is added next to the exit and the puzzle is in a hopefully solvable configuration. Every button and every catcher does something. Initial tests with my brother go well, and the new layout seems to fit in well with the difficulty curve again. It's still difficult, but much easier than it was before.
I speculate that reports of chamber 30's difficulty are a bit exaggerated, but can't quite confirm them. I'm at least somewhat sure that people unable to solve it were just recovering from the difficulty spike burning their brains out. I've had mixed feelings about changing this chamber alone, but decided to do so because it's just too damn hard. The original version is now preserved as 29 Advanced. The only changes that will be made to that will be the removal of one line of GLaDOS dialogue, along with the title (adding "Advanced") and changing the chamber entry sign. The elevators will also need to be unlinked from the other chambers, and it must be designed to show its status as "completed" upon doing so. Most of these are things the average player won't even think about, but you do in fact need to add entities to the map to control advanced chambers. As these changes will preserve all challenges and in the effort of keeping the mod's more skilled players pleased, a series of "Advanced Challenges" are planned, which will add the least portal, least step, and least time challenges to all advanced chambers. Other changes are planned for other chambers, but these are all either cosmetic or to fix glitches. I begin to speculate wildly on a release date. The practical range is somewhere between September 30th and Portal 2's release, which at this time is in February 2011.
DAY 5: Lightstrips, bumpers
Blue and yellow paths now connect relevant puzzle elements. Shooting portals on concrete walls adjacent to metal walls now bumps the portal so that it is fully on the concrete wall, instead of causing the placement to fail. This is all to prepare for the first beta test of the new level, which will be done with a friend who almost tried to strangle me when playing the old #29. PROTIP: Don't give your maps to anyone to playtest and stand behind them as they play if they can run faster than you.
DAY 6: Replacing a fling
While one section in this map needs to be traversed only once, my (two) playtesters both had an annoying habit of passing it multiple times. This section used the infinite fling technique which is hard enough as is. The section is replaced with an angled double fling.
DAY 7: Details, details, details
A few things are tweaked based on more test feedback. Cubemaps are added and two previously empty observation rooms are filled with objects. Security cameras and signs are placed in strategic locations throughout.
BEYOND: Ignorance, apathy, then the rest
One important step in making these chambers was to ignore them for extended periods of time and work on other levels. In this case, I have 21 and 25 Advanced to fall back to. When coming back, I have fresh ideas and newfound mapping skills. At that time, I'll test it again and perhaps change the layout a bit more before final release. Hopefully, I'll have done something right this time.
Level 29 was to hard for most people?
I didn't find it that hard.