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