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.
Speak to all of the spirit animals.
Find Erin when she's gone.
Completed the game.
Complete the Eventide Sanctuary.
Step into the well.
Find the Crab Island.
Find the statue of the deer.
Get some Lambaby love.
Complete the Monastery.
Find the Ancient Llamba.
Complete the Archives.
Find the statue of crane.
Discover all areas of the map.
Find the chiseled stone map.
Find the giant birdshrine.
Find the statue of the fox.
Find the ancient battlefield.
Find the dwellings of the rift cult.
Find the bones of an old beast.
Escape the collapsing cave.