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