Halloween is coming...
What would make a scary map for Halloween?
I'm currently testing with... well, I won't spoil it. 
My Work
[spoiler]Maps:
Revenge of the Angry Turrets
Capture the Cube [Co-op]
Capture the Cube 2 [Co-op]
TPWEGTH Sample Map
Aperture Aquatic Testing Center
Aperture Aquatic Testing Center 2
Aperture Time Testing Center
ML's Halloween Trick - 1000 downloads!
ML's Halloween Treat
ML's Combination - 1000 downloads!
ML's Jailbreak Labyrinth
ML's Tricky Teamwork [Co-op]
WIP:
"Capture the Cube 3"
Workshop Maps Link: http://steamcommunity.com/profiles/76561198008890579/myworkshopfiles/[/spoiler]
Alot of misaligned textures is kinda scary.
PortalStories.com
"Oh, in case you got covered in that repulsion gel, here's some advice the lab boys gave me: DO NOT get covered in the repulsion gel."
Like a deformed test chamber or are you being a wiseguy?
My Work
[spoiler]Maps:
Revenge of the Angry Turrets
Capture the Cube [Co-op]
Capture the Cube 2 [Co-op]
TPWEGTH Sample Map
Aperture Aquatic Testing Center
Aperture Aquatic Testing Center 2
Aperture Time Testing Center
ML's Halloween Trick - 1000 downloads!
ML's Halloween Treat
ML's Combination - 1000 downloads!
ML's Jailbreak Labyrinth
ML's Tricky Teamwork [Co-op]
WIP:
"Capture the Cube 3"
Workshop Maps Link: http://steamcommunity.com/profiles/76561198008890579/myworkshopfiles/[/spoiler]
That would make me scream for at least 10 hours!
Like a deformed test chamber or are you being a wiseguy?
Are those the only choices?
PortalStories.com
"Oh, in case you got covered in that repulsion gel, here's some advice the lab boys gave me: DO NOT get covered in the repulsion gel."
I want to see "the chamber [GLaDOS] built where all the robots scream at you." Now there's your Halloween map.
Darkness... If you have played amnesia, you know what i mean... NOT totalt darkness. The player may just not have a chance to see the whole level at once...
Then voices, coming out of nowhere...
Stuff like eyes popping up and disappearing again...
Make a normal test chamber where you get in and suddenly something goes wrong and all light goes out... And somebody is being released... What if glados and wheatley Found together to get rid of you?
Search "female" or "male" in the model browser... Maybe you can use Them. Maybe there is a mad scientist somewhere in the map?
EDIT: And the env_fire! Fire is always scary! make the fire come out of nothing, with no other purpose than lighting your way... 
Actually you gave me ideas... I will be starting too... Where are you putting a map like that?
Then voices, coming out of nowhere...
Stuff like eyes popping up and disappearing again...
Make a normal test chamber where you get in and suddenly something goes wrong and all light goes out... And somebody is being released... What if glados and wheatley Found together to get rid of you?
Search "female" or "male" in the model browser... Maybe you can use Them. Maybe there is a mad scientist somewhere in the map?
EDIT: And the env_fire! Fire is always scary! make the fire come out of nothing, with no other purpose than lighting your way...
Actually you gave me ideas... I will be starting too... Where are you putting a map like that?
That sounds cool, I'd play a map like that.
Sphere. May the best sphere win. Swap that in. Much more clever. Books."
Check me out on deviantART! http://cookieninja8.deviantart.com/
The idea of using fire to light your way could be cool. If you could make some kind of torch the player carries around, which sometimes needs to be set down in order to complete parts of the test. It would have to light the immediate area pretty well, to avoid frustration, but it could leave the rest of the map dark.
Thanks for over 1,000 downloads: The Cold Shoulder
Maybe you have to carry around the partially incinerated companion cube from Portal 1?
(CO-OP) Orb Facility (Updated as of February 14th 2012, v1.06)
(CO-OP) Impetuosity (Updated as of April 18th 2012, v1.15)
(CO-OP) Puffin (Updated as of March 6th 2012, v1.06)