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