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