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