This is a comprehensive guide on how to unlock the Glass Door and Fail Door achievements. It provides hints and the solution (with spoiler text) in case you just need a little boost and still want to solve the puzzles on your own.
Glass Door
After first entering the Winter area, the door is on the left hand side of the fifth puzzle. If you reached the piano, you’ve gone too far.
It has three horizontal glass panes across the middle with a crescent move above it.
Hints
The door has nothing to do with the environment around it.
What time of day is the moon normally out?
The position of the moon (directly above the door) is related to a clock.
Fail Door
Once you reach the sign labeled “exit at the door with figure ?”, go through the left-most gate twice in a row.
You will see the letter ‘R’ on your screen, indicating you have failed the puzzle, hence the name “Fail Door.”
On the left, you should see the Fail Door.
Hints
The door has nothing to do with the environment around it.
It is called the FAIL door.
The door has numbers on them: 1-5.
What other door deals with numbers & even has a number on the starting door?
The X’s have a specific meaning related to failing.
Answer
• Go into the desert door.
• Fail each door in order 1-4. If the sign matches the door (i.e., you don’t fail when you walk through), just fail at the next door in the puzzle (A=1, B=2, C=3, D=4).
• Once you fail those four doors in order, head to the fail door in the shape garden.
• Your fifth & final fail should be entering the dead end with the fail door & the door will be open.