Here is the full list of all 20 AER - there are Memories of Old achievements. It takes around 3-4 hours to unlock all of the achievements on Windows.
Completed the game.
Complete the Eventide Sanctuary.
Discover all areas of the map.
Complete the Monastery.
Complete the Archives.
Find the statue of crane.
Find the statue of the deer.
Step into the well.
Escape the collapsing cave.
Find the Ancient Llamba.
Speak to all of the spirit animals.
Get some Lambaby love.
Find Erin when she's gone.
Find the Crab Island.
Find the bones of an old beast.
Find the dwellings of the rift cult.
Find the ancient battlefield.
Find the chiseled stone map.
Find the giant birdshrine.
Find the statue of the fox.