The City of Aquatica is a domed city on Eternia. It is located beneath the Harmony Sea.
Princess Nami was the ruler of the City of Aquatica. She was captured by Mer-Man, who took posession of her kingdom and the Pearl of Power, which he used to put a spell on the Aquaticans. He then ordered the princess to be imprisoned in the Coral Caverns where she was guarded by a large sea creature.
He-Man and Man-At-Arms swam into the cave where she was being kept and He-Man defeated the Coral Creature by causing a cave-in. Back in Aquatica they managed to get the Pearl back and the princess restored her people to normal, but Mer-Man decided to destroy the city with his whirlpool machine. He-Man manages to spin a guard rail on the edges of the city fast enough that it destroyed the whirlpool, saving Aquatica.