Here is the full list of all 12 Inmates achievements.
Complete the Game
Meet Ben for the final time
Solve the "Sound Trap" puzzle
Get discovered by the pop up creature
Pass the second subconscious level
Pass the first subconscious level
Meet Ben for the first time
Find the half of the photo with Sarah on it
Solve the "Time Trap" puzzle
Find the inmates list
The nightmare begins
Pass the third subconscious level