Stormbreaker Whirlpool, also known as the Mirage Vortex, is the largest of Windworth Island's whirlpools. It is powered by extremely high winds. Stormbreaker Whirlpool is responsible for the creation of the island. It is called the Mirage Vortex because some ill-fated ships have seen a white mist rise from it. They then have horrible hallucinations.
The only creature ever to survive Stormbreaker Whirlpool is the Spirit of Terraria, which traveled into it to see what the secret of the whirlpool is. They came out alive, but still do not speak of what happened inside. All that is known is that it did battle with a malevolent entity of much power.