Full list of all 28 Portal Stories: Mel achievements. It takes around 6-8 hours to unlock all of the achievements in the base game on Windows.
The base game contains 27 achievements, and there is 1 DLC pack containing 1 achievements.
Mind your Step
Get into the vents
Check that all doors have been locked for the night
Shut down AEGIS in Advanced Mode
Reach AEGIS's Domain
Get shot on the turret range
MAKE IT STOP
Get crushed in the door
Get off the track again
Solve the broken test
Get burned whilst in the goo
Not even all the way!
Try to bring the cube with you
Hide from AEGIS
Solve the same test three times!
Ignore good advice
Find the radio under the stairs
Enter Virgil's testing track
Get electrocuted
Refuse to Listen
Discover a new way to turn down the heat
Who is that?
Experience a Deeply Unimpactful Moment
Find all the Vitrified door messages
Oversleep
Super Drowning Skills
Enter the main lobby of Aperture Science Innovators
Shutdown AEGIS in Story Mode