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