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