No missable achievements (plus 15 unknown)
Sign in with Steam or Xbox to track your progress, and:
Acquire the fully powered Aperture Science Handheld Portal Device.
Do whatever it takes to survive.
Make the correct party escort submission position decision.
Knock down a turret with another turret.
Beat two Portal advanced maps.
Jump 300 feet.
Beat four Portal advanced maps.
Beat all six Portal advanced maps.
Fall 30,000 feet.
Detach security cameras from the walls.
Earn silver medals on all Portal challenges.
Earn bronze medals on all Portal challenges.
Earn gold medals on all Portal challenges.