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