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