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