Snorra Edda. "The Deluding of Gylfi".
The conception of Jotunheim was chosen to introduce some of ancient Scandinavian believes:
"'That part of Ginnungagap which turned northwards became full of the ice and the hoar frost's weight and heaviness, and within there was drizzling rain and gusts of wind. But the southern part of Ginnungagap became light by meeting the sparks and glowing embers which flew out of the world of Muspell...
and where the soft air of the heat met the frost so that it thawed and dripped, then, by the might of that which sent the heat, life appeared in the drops of running fluid and grew into the likeness of a man. He was given the name Ymir, but the frost ogres call him Aurgelmir, and that is where the families of frost ogres come from..."