Take-Off
Take-Off is a large, highly tested and polished custom level for Portal 1. Brimming with big secrets, custom models, and custom textures, Take-Off is almost certainly unlike any Portal map you have ever played. The observant player will find that the scope of Take-Off is much greater than just a Portal test-chamber.
This map is designed to be a moderate challenge for experienced players (Portal, Portal: The Flash Version/Still Alive, at least.) The difficulty ramps up significantly within the level. Solutions to puzzles NEVER require cheats or exploits, and all playable parts of the map are designed and tested to be reachable *without cheats.*
Once figured out, the solutions to puzzles in this map are designed to be as easy to execute as possible. However, given the types of puzzles in Take-Off, some finesse with control will be required. The required control should not be a problem for experienced players.
Take-Off includes the three challenges: Time, Steps and Portals. Getting the gold in Time and Steps will likely not pose a huge challenge for those who have completed the level, and are experienced in these types of challenges. The gold in Portals, however, is a serious challenge, and will be very difficult for virtually all players. I assure you, it IS possible to get the gold without cheats, just very hard.
Aesthetically, Take-Off is deliberately clean. I have, in general, avoided grungy accents and opted for a "perfect," streamlined look. Except where noted in the in-game credits, I created all custom props from scratch. Except where noted, I either created custom materials from scratch, or modified Valve's materials.
I think that those who play this map to its full potential, will find that it is a unique experience they won't soon forget. : )
Enjoy!
Sword of Apollo
[Note: Take-Off v1.1 is identical to v1.0, except that one extra portal cleanser has been added to remove an exploit I just discovered.]
[Note: Take-Off 1.2 fixes the fact that the player could put a portal on the inside of the raised glass box in the large chamber. This is not an intended solution to getting to the last button, but an embarrassingly bad oversight on my part.]
[Note: Take-Off 1.3 has a slightly longer timer late in the level, a few exploit fixes, and secrets that are made slightly more obvious. One green fizzler that used to dissolve objects no longer does.]
[Note: Take-Off 1.4 is identical to 1.3, except that one part of a secret puzzle has been made easier and hopefully less frustrating to do, (physically.)
Take-Off 1.4.1 fixes a couple of model texture issues in the secrets.]
[Note: Take-Off 1.5 adds a functionality bug fix for secrets. If you downloaded v1.5 prior to 6/24/11, please redownload and reinstall, because I accidentally left items in the map that I used for testing. The prior release of 1.5 definitely will NOT play as intended.]
[Note: In Take-Off 1.6, a secret puzzle now works exactly as intended, (instead of approximately.) A portion of this puzzle is now slightly easier.]
[Note: In Take-Off 1.7, a couple of unintended solutions in the main level have been eliminated (or as close as possible.)]
[Note: v1.7.1 makes getting to one of the secrets easier than in all previous versions. The update to 1.7 had the side-effect of making it excessively hard to get to.]
File Name: Take-Off 1.7.1.zip
File Size: 133.89 MiB
Click here to download Take-Off
Very, very, VERY nicely done. Of course, I'm stuck in the very large chamber with the first energy pellet. But I was extremely impressed simplpy by the textures and the room with the blue book. Being so used to Portal 2 mechanics by now, it's refreshing to have more mobility with the portal gun.
Thanks, I'm glad you like the textures in the beginning. 
As you may have guessed, what you have seen is the tip of the iceberg of custom content. 
Looks very good and it was fun but I am stuck in the exact same room. I have the cube from previous chambers with myself but I have absolutely NO IDEA where to go next or what to do. It seems I cannot get anywhere even by flinging and the same with the energy pellet. Please give us a clue!
Also, I haven't found any secrets yet, did I miss something 
(percentage calculation sphere self-test failed!)
108.1% done, -8.1% remaining...
Released here!
All maps for Portal (1/2) worth playing are mirrored here.
Awesome map! That last room is kinda scary indeed, but mostly cause of its size. After you take the first step, everything is pretty clear. To people having problems:
Please, do. There are only 2 angled surfaces and both get the pellet nowhere.
I am so dumb or what I can't figure it out myself for god's sake 
(percentage calculation sphere self-test failed!)
108.1% done, -8.1% remaining...
Released here!
All maps for Portal (1/2) worth playing are mirrored here.
Please, do. There are only 2 angled surfaces and both get the pellet nowhere.
I am so dumb or what I can't figure it out myself for god's sake
EDIT: The images are spoilers of the solution, everyone stay away from them if you don't want to get spoiled. Even if it's quite obvious, i'm mentioning it just in case.
Hehe, ok. I took a couple of pics for the first part of the puzzle...
The first pair of portals:
After the pellet comes out, the second pair:
If you are fast enough,
Thank you 
(percentage calculation sphere self-test failed!)
108.1% done, -8.1% remaining...
Released here!
All maps for Portal (1/2) worth playing are mirrored here.
The secrets are well hidden, and I'd suggest just trying to get through the map on the first play-through. Once you know the map, if you want to find secrets, put yourself partially in the mindset of a game tester.
I just updated to v 1.1 with the addition of a single portal cleanser before the "fizzler hall." It doesn't change anything, except that you can no longer take the cube further into the level. When Mek mentioned that he had taken the cube with him into the large chamber, I realized that this was a weak spot in my testing, and decided to check this.
A lot of players would find that the cube doesn't help them in that chamber, and if that were the case for ALL players, I would have left the map as is. But I did find an exploit that really adept players can take advantage of to bypass a puzzle. This makes it too easy to get gold in the minimum portals challenge, so I decided to strip the player of the cube after it has served its intended purpose.
Sorry for the inconvenience, but if you really want credit for the gold on minimum portals, you're going to have to do it without the cube beyond the point where the new fizzler is.
Anyway, thanks for the compliments on my map, soad667. Please tell us if you find any secrets. (Just not too specifically without spoiler tags, of course. )