Here is the full list of all 20 The Guest achievements.
Get to the end.
Write BENEFACTOR on the typing machine.
Type the password in the computer.
Get into the secret room.
Locate the Team Gotham's headquarter.
Complete the music puzzle without failing.
Read all the newspapers.
Listen to some music on the record player.
Collect all possible objects.
Complete the dream maze scene withouth failing.
Turn off all the lights.
Use the sign and don't be disturbed.
Try lighting a cigarette.
Enter the toolbox password without combining the notes.
Wait 8 hours and hit the button again.
Complete the valves puzzle in less than 20 movements.
Try consuming the bath pills again.
Call every single number on the phonebook.
Be thankful twice.
Solve the batteries puzzle in just 2 movements.