From a dialogue about the beginning of the world; at one point, a giant called Ymir is mentioned:

“Where did Ymir live, and what did he live on?”

“The next thing, when the rime dripped, was that there came into being a cow called Audhumla, and four rivers of milk flowed from its teats, and it fed Ymir.”

Then spoke Gangleri: “What did the cow feed on?”

High said: “It licked the rime-stones, which were salty. And the first day as it licked stones there came from the stones in the evening a man’s hair, the second day a man’s head, the third day there was a complete man there. His name was Buri. He was beautiful in appearance, big and powerful. He begot a son called Bor. He married a wife called Bestla, daughter of the giant Bolthorn, and they had three sons. One was called Odin, the second Vili, the third Ve. And it is my belief that this Odin and his brothers must be the rulers of heaven and earth; it is our opinion that this must be what he is called. This is the name of the one who is the greatest and most glorious that we know, and you would do well to agree and call him that too.”

Then spoke Gangleri: “How did they get on together, which group was more powerful?”

Then High replied: “Bor’s son’s killed the giant Ymir. And when he fell, so much blood flowed from his wounds that with it they drowned all the race of frost-giants, except that one escaped with his household. Giants call him Bergelmir. He went up on to his ark with his wife and was preserved there, and from them are descended the families of frost-giants, as it says here:

Countless winters before the earth was created, then was Bergelmir born. That is the first I remember, when that wise giant was laid on a box.

Then Gangleri replied: “What did Bor’s sons do then, if you believe that they are gods?”

High said: “There is not just a little to be told about that. They took Ymir and transported him to the middle of Ginnungagap, and out of him made the earth, out of his blood the sea and the lakes. The earth was made of flesh and the rocks of the bones, stone and scree they made out of the teeth and molars and of the bones that had been broken.”

Then spoke Just-as-high: “Out of the blood that came from his wounds and was flowing unconfined, out of this they made the sea which they encompassed and contained the earth, and they placed this sea in a circle round the outside of it, and it will seem an impossibility to most to get across it.”

Then spoke Third: “They also took his skull and made out of it the sky and set it up over the earth with four points, and under each corner they set a dwarf. Their names are Austri, Vestri, Nordri, Sudri. Then they took molten particles and sparks that were flying uncontrolled and had shot out of the world of Muspell and set them in the middle of the firmament of the sky both above and below to illuminate heaven and earth. They fixed all the lights, some in the sky, some moved in a wandering course beneath the sky, but they appointed them positions and ordained their courses. Thus it is said in ancient sources that by means of them days were distinguished and also the count of years, as it says in Voluspa:

The sun did not know where her dwelling was. The moon did not know what power he had. The stars did not know where their places were.

That is what it was like above the earth before this took place.”

Then spoke Gangleri: “This is important information that I have just heard. That is an amazingly large construction and skillfully made. How was the earth arranged?”

Then High replied: “It is circular round the edge, and around it lies the deep sea, and along the shore of this sea they gave lands to live in to the race of giants. But on the earth on the inner side they made a fortification round the world against the hostility of giants, and for this fortification they used the giant Ymir’s eyelashes, and they called the fortification Midgard. They also took his brains and threw them into the sky and made out of them the clouds, as it says here:

From Ymir’s flesh was earth created, and from blood, sea; rocks of bones, trees of hair, and from his skull, the sky.

And from his eyelashes the joyous gods made Midgard for men’s sons, and from his brains were those cruel clouds all created.”

– “Gylfaginning,” in the Prose Edda,

translated by Anthony Faulkes, Edda, 11-13

Read the other Great Myths here