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