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