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.
Find the statue of the deer.
Escape the collapsing cave.
Complete the Eventide Sanctuary.
Complete the Archives.
Complete the Monastery.
Completed the game.
Find the Ancient Llamba.
Speak to all of the spirit animals.
Discover all areas of the map.
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.
Find the statue of crane.
Step into the well.