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