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 bronze medals on all Portal challenges.
Earn silver medals on all Portal challenges.
Earn gold medals on all Portal challenges.
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Detach security cameras from the walls.
Jump 300 feet.
Beat all six Portal advanced maps.
Beat four Portal advanced maps.
Beat two Portal advanced maps.
Complete Portal.
Knock down a turret with another turret.
Make the correct party escort submission position decision.
Do whatever it takes to survive.
Fall 30,000 feet.
Acquire the fully powered Aperture Science Handheld Portal Device.