Here is the full list of all 31 A Castle Full of Cats achievements. It takes around 1-2 hours to unlock all of the achievements on Windows.
Release Fofiño from the curse
Find all cats in the pantry
Find all the cats
Meet everyone at the final door
Return all the kittens to mama cat
Find all the keys
Find all cats in the trapdoor
Find all cats in the secret trapdoor
Help a friend from the underground
Deliver the snack
Find all cats in the library
Find the crystal ball upgrade
Find all cats in the saferoom
Open the passage
Find all cats in the bedroom
Find the hidden castle map
Unlock a magical shortcut
Find all cats in the mirror passage
Find all cats in the underground corridor
Find all cats in the cemetery
Find all cats in the laboratory
Find all cats in the cell IV
Find all cats in the cell III
Find all cats in the cell II
Find all cats in the cell I
Find all cats in the dungeons
Find all cats in the kitchen
Find all cats in the main hall
Find the castle map
Find all cats in the castle
Find the crystal ball