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