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