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