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