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