Here is the full list of all 15 Looking Up I See Only A Ceiling achievements.
While looking for a way to enter the Bathroom, read all of your exams' notes.
Check the Bathroom’s shower before going up.
Unlock the Secret Ending.
Talk 3 times to the man while he’s working before leaving his place.
Interact with ALL the points of interest in the Explore Mode.
Find the authors of the game working in the Explore Mode.
Access the Explore Mode.
Unlock both "Bad Ending" and "Good Ending".
Reach Checkpoint V-A.
Reach Checkpoint V-B.
Reach Checkpoint IV.
Reach Checkpoint III.
Reach Checkpoint II.
Reach Checkpoint I.
Do only wrong actions during the breakfast mini-game three times in a row.