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