Here is the full list of all 15 Portal achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Earn silver medals on all Portal challenges.
Earn gold medals on all Portal challenges.
Earn bronze medals on all Portal challenges.
Jump 300 feet.
Beat all six Portal advanced maps.
Fall 30,000 feet.
..?
Detach security cameras from the walls.
Beat four Portal advanced maps.
Make the correct party escort submission position decision.
Complete Portal.
Beat two Portal advanced maps.
Do whatever it takes to survive.
Acquire the fully powered Aperture Science Handheld Portal Device.
Knock down a turret with another turret.