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