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 5
Finish Level 4
Finish Level 3
Make dancing three friends
Finish Level 2
Find the children in the wood
Win "Hide and seek"
Finish Level 1
Finish Level 6
Finish Level 7
Finish Level 8
Finish Level 9
Finish Level 10
Finish Level 11
Finish level 12
Finish level 13
Find the sentence
Play the good melody for the first time
Speak with everyone
Sort them