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