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