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