Here is the full list of all 18 Uninvited Guest achievements.
Do not be afraid, everything is fine
Start the game
Collect all the gold figurines in the first level
Complete the first level
Complete the second level
Complete the third level
Complete the fourth level
Complete the game
Read all the notes on the first level
Read all the notes on the second level
Read all the notes on the third level
Read all the notes on the fourth level
Read all the notes on the fifth level
Collect all the gold figurines on the second level
Collect all the gold figurines on the third level
Collect all the gold figurines on the fourth level
Collect all the gold figurines on the fifth level
You have found a rare painting