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