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