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