Hafgufa

Hafgufa (Icelandic, haf "sea" + gufa "steam") is the name of a massive sea monster reported in the Örvar-Odds saga to have existed in the Greenland Sea which was said to disguise itself as an island or pair of rocks rising from the sea.

Norway

In Konungs skuggsjá, an Old Norwegian philosophical didactic work written toward the end of the 12th century, the King told his son of several whales that inhabit the Icelandic seas, concluding with a description of a large whale that he himself feared, but he doubted anyone would believe him about without seeing it. He described the Hafgufa (Hafgufu in Old Norwegian language) as a massive fish that looked more like an island than like a living thing. The King noted that Hafgufa was rarely seen, but always seen in the same two places. He concluded there must be only two of them and that they must be infertile, otherwise the seas would be full of them.

The King described the feeding manner of Hafgufa: The fish would belch, which would expel so much food that it would attract all the nearby fish. Once a large number had crowded into its mouth and belly, it would close its mouth and devour them all at once.