Charybdis was a Greek sea monster of terrifying proportions.
History[]
Charybdis was a nymph born out of union of Poseidon and Gaia. When her father had quarrel with Zeus, Charybdis supported Poseidon to an extent that didn't please Zeus. As Charybdis had been tasked with flooding dry lands, the king of the gods cursed her to become a gargantuan monster to live beneath a rock at the Strait of Messina. There she would forever swallow water three times a day, creating periodical whirlpools that threatened to sink entire ships.

Charybdis and Scylla in painting by Johann Heinrich Füssli
Other side of the strait was not safe either, as another monster, Scylla, lived there. Anyone wishing to pass through had to decide if it was worth it to risk losing whole ship, or to lose some of the crew for certain.
Appearance[]
After Zeus had curse Charybdis, she became an enormous monster that mostly consisted of a bladder, with flippers and fins as arms and legs.