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