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