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