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