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