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