Here is the full list of all 20 Three Twenty One achievements.
Use the printer in the text adventure
Listen to the radio
Take the horse with you on the boat
Finishing Castle without dying
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Taking the bear in the text adventure
Play 3:21 again
Read through the friend book
Complete the game
Visit the PT area
Play Void
Fail CodeCrashers
Read through the viking book
Examining the football picture in the bedroom
Collect all the books
Find the secret space room
Taking the letter
Listen to all audio recordings
Leave everything behind