Here is the full list of all 27 Aquaria achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Travel to all the areas of Aquaria.
Find all the Ancient Turtles.
Learn all the songs in Aquaria.
Rescue all the lost souls.
Defeat Mom and Dad.
Defeat the King Jelly.
Find all the health eggs.
Reach the Frozen Veil.
Find all the recipes in the game.
Enter the belly of the Whale.
Discover two peculiar-looking fish...
Beat the Arnassi race in less than a minute.
Fling a Monkey.
Defeat the Priests.
Defeat Octomun.
Defeat Mergog
Reach the Sprite Cave.
Kill the Coward.
Dive into the water from a certain high location...
Devour a Parrot.
Devour 6 creatues in a row.
Ride Ekkrit for a minute.
Reach Open Waters.
Defeat the Rock Crab.
Defeat the Mantis Shrimp.
Reach the Veil.
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