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