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