Here is the full list of all 21 Seasons after Fall achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Find a place to sleep.
You're not alone anymore...
Use the Summer fragment to reveal this fresco.
Use the Spring fragment to reveal this fresco.
Use the Autumn fragment to reveal this fresco.
Use the Winter fragment to reveal this fresco.
What's on the surface?
Enter an unfamiliar place.
Return to an unfamiliar place.
Bring "something very precious" to the Sanctuary.
It's not quite the end.
The End.
Activate this altar to invoke the Guardian of Winter.
Activate this altar to invoke the Guardian of the Fall.
Activate this altar to invoke the Guardian of Spring.
Activate this altar to invoke the Guardian of Summer.
Find the bird, listen carefully and keep very still.
Explore and make all the flowers bloom.