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.
Oversleep
Enter the main lobby of Aperture Science Innovators
Who is that?
Discover a new way to turn down the heat
Enter Virgil's testing track
Check that all doors have been locked for the night
Super Drowning Skills
Try to bring the cube with you
Solve the same test three times!
Hide from AEGIS
Get off the track again
Reach AEGIS's Domain
Shut down AEGIS in Advanced Mode
Find the radio under the stairs
Experience a Deeply Unimpactful Moment
Not even all the way!
Get burned whilst in the goo
Get crushed in the door
Get shot on the turret range
Get electrocuted
Get into the vents
Refuse to Listen
Mind your Step
Ignore good advice
Find all the Vitrified door messages
Solve the broken test
MAKE IT STOP
Shutdown AEGIS in Story Mode