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