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