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