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.
Complete the Eventide Sanctuary.
Discover all areas of the map.
Find the bones of an old beast.
Find the Ancient Llamba.
Find the dwellings of the rift cult.
Speak to all of the spirit animals.
Find the ancient battlefield.
Find the chiseled stone map.
Find the statue of the fox.
Find the giant birdshrine.
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.