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