One in the Chamber
One in the Chamber is a single player map built specifically for the ThinkingWithPortals.com Summer Mapping Initiative.
The name "One in the Chamber" refers to the amount of cubes available to complete the chamber. The map is built with the Destroyed Aperture theme in mind, and contains two puzzle rooms, as well as an introductory corridor. The difficulty level has been kept low to medium, to allow players a challenge without wanting to pound there fist into their monitors.
All mappers feel free to rifle through the .vmf for fog/lighting settings, and the likes, as well as to learn how I put the level together.
filename: sp_1_inthechamber.bsp
Screenshot: http://interlopers.net/titan/sp_1_inthechamber0003.jpg
KrispyTheKorn aka, IZaNaGI
Update:
Re-uploaded with missing readme file.
Update 2:
Fixed an issue allowing players to complete the final room in an unintended fashion.
Added "info_placement_helper" entity's to some white surfaces as per player feedback.
Replaced an errant "cool" light instance with a "warm" instance.
Update 3:
Fixed "black" textured surfaces so that they are no longer portalable (if that's even a word ... which it isn't).
File Name: sp_1_inthechamber050611_03.zip
File Size: 19.86 MiB
Click here to download [SP] One in the Chamber
Very good, one of the best so far.
I don't think I solved it correctly. On the last part of the chamber I was able to get some blue stuff on the platform next to the water gel. However, I could not find any way to use this, so I just bounced up with the block to beat it.
Well one way is as good as the other i suppose 
but the way the map was intended to be completed
Apologies for not making the true solution more obvious!!
You should really use info_target entities and placement helpers. Right now, the map is harder to solve than it should be. I took quite a bit of time trying to get back up to the platform in the end.
I'm not aware that there are "Placement Helpers" available in the sdk (This is my first Portal 2 map), saying that though i wasn't aware that it was particularly difficult to gain access to the highest level.
I'll look into implementing helpers if it turns out a bigger problem than I had envisioned.
Thanks for playing though, even if you found it frustrating. That was not my intention!
Fantastic map! Love the attention to detail. For me, I also solved the final chamber in an unintended way.
LOL Wow great find. I'll try to patch that before the end of the day, and thank you for the kind words!
I just loved the atmosphere, and the skybox was pure win.
Also, there are placement helpers, which are called "info_placement_helper". 
5/5 all around.
Thanks bud. I've added placement helpers (as well as made some other small changes), and i'm currently uploading an updated version as per player feedback.
If any other issues arise please let me know!
Thanks everyone.