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