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