Here is the full list of all 20 Sanitarium achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Finish Level 2
Win "Hide and seek"
Find the children in the wood
Finish Level 1
Finish Level 3
Finish Level 4
Finish Level 5
Finish Level 6
Finish Level 7
Finish Level 8
Finish Level 9
Finish Level 10
Finish Level 11
Finish level 12
Finish level 13
Make dancing three friends
Find the sentence
Play the good melody for the first time
Speak with everyone
Sort them