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