Poseidon's Boneyard

Poseidon's Boneyard is where the former Queen and King of Arendelle are caught in a storm and drowned when on their way back from an expedition to the Enchanted Forest.

Before the Curse
Lightning flashes amidst the night sky as rain thrashes down on the stormy sea below, on top of which a ship is struggling to sail, being tossed about by the enormous waves. Its flag blows wildly as its crewmen try in vein to keep it steady, but still water continues to gather. Below deck, which is beginning to flood, a woman in a crown - the Queen of Arendelle - bursts forth from a doorway and heads over to a stationery set, from which she eventually manages to find a pen to write something down on a sheet of paper. As she writes, her husband - the King of Arendelle - begins descending the stairs in search of her and asks her what she's doing, reluctant to approach due to all the water. His wife exclaims that she has to finish "this", but he speaks out against it, managing to make his way over to her as he tells her that the vessel is going down and they have to abandon ship. She simply continues writing and replies, "They have to know." She then finishes her note and rolls it up in her hands, pointing out that, while they might not may it home, this could. The King is wearisome. With the message now enclosed in a glass bottle, the King and Queen make their way above deck, trying their very hardest, under these conditions, to make a few small steps. The King asks his wife if she's sure they're doing the right thing, and she answers positively, saying that Anna and Elsa must know the truth; it's the only thing that will save them. With that, the King hurls the message in a bottle out at sea and the royal couple look on as their ship is enveloped by water.

Season 4
Thirty years after Arendelle was struck by Ingrid, Anna, Kristoff and all others in the kingdom finally unfreeze, which means Hans and his brothers are also free to attack the princess and her fiancé. They manage to escape, however, and decide to locate the pirate Black Beard so that they can pay him with their riches for something called the wishing star, which Anna read about in her mother's diary. Soon after they arrive on the ship and make their offer, Hans and his brothers show up yet again, having robbed the royal treasury and made their own deal with Black Beard beforehand. The pirate then sails them all out to the same spot where Anna's parents' boat sank and, per Hans' directive, the two of them are sealed in a chest and thrown overboard. Water begins filling the chest and it seems as though the engaged couple is about to drown, and so Anna tries marrying Kristoff before they both die. He refuses, however, saying that they can get married when they get out of this and, soon enough, the two of them are transported to the town of Storybrooke by Elsa, who used the wishing star (which turns out to be Anna's necklace) to wish for them to be there.