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.
The End.
Find a place to sleep.
It's not quite the end.
Activate this altar to invoke the Guardian of Spring.
Bring "something very precious" to the Sanctuary.
Activate this altar to invoke the Guardian of Summer.
Activate this altar to invoke the Guardian of Winter.
Return to an unfamiliar place.
Activate this altar to invoke the Guardian of the Fall.
You're not alone anymore...
Enter an unfamiliar place.
Use the Winter fragment to reveal this fresco.
Use the Autumn fragment to reveal this fresco.
Use the Spring fragment to reveal this fresco.
Use the Summer fragment to reveal this fresco.
What's on the surface?
Find the bird, listen carefully and keep very still.
Explore and make all the flowers bloom.