Here is the full list of all 15 Portal achievements. It takes around 10-12 hours to unlock all of the achievements on Windows.
Beat all six Portal advanced maps.
Beat four Portal advanced maps.
Beat two Portal advanced maps.
Earn gold medals on all Portal challenges.
Earn bronze medals on all Portal challenges.
Earn silver medals on all Portal challenges.
Jump 300 feet.
..?
Detach security cameras from the walls.
Do whatever it takes to survive.
Fall 30,000 feet.
Acquire the fully powered Aperture Science Handheld Portal Device.
Make the correct party escort submission position decision.
Complete Portal.
Knock down a turret with another turret.