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