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