The Crystal Sea was a large mass of water located on Eternia that was decorated by ice formations resembling large crystals.

There was once a great kingdom ruled by Squidish Rex, King of the Aquaticans, within the sea but it was destroyed in a battle with rival ocean clans, making the city uninhabitable. The all knowing Oracle of the Crystal Sea was known to reside in a cave in the Crystal Sea. However, getting there was dangerous, as Shadow Beasts roamed the area. The Shaping Staff was also hidden there before being found by Evil-Lyn and Beast Man. One had to traverse the Crystal Sea to reach the gates of Subternia.