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