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