OC Note: The information here is based on rumours and memories and should be treated as reliable as they would appear to your characters.
Few firm and consistent details have survived on Midgard about Jotunheim, except to say that it is the home of the Jotnar. However those gods who remained in Asgard remember the realm of their ancient antagonists (as it stood over a thousand years ago) with much more clarity.
“One of the grandest of the Nine Worlds, that sits in the upper branches of Yggdrasil; Jotunheim was the land of the Giants, ancient rivals of the Aesir. To the most recent of our knowledge, the landscape of Jotunheim is bleak and unforgiving; with Longhouses belonging to the various Jotunn Lords being the only respite dotting the sheer cliffs and dark, dense forests. The Jotnar themselves were a proud and solitary sort and our surviving history of their squabbles and conflicts with the Gods of the Norse people often belittles a sort of idiosyncratic honour that is present in older, source texts.”
- Excerpt from The Nine Worlds, a Primer to Norse Mythology.
Most Eddic and Heathen sources refer to Jotunheim as being a barren taiga: with intermittent areas of tundra plain and snow capped mountains breaking up the dense forest that covers most of the Realm.
The Aesir remember this land far more clearly: enough to confirm the Eddic tales and more. The Jotnar lived in secluded longhouses, which rarely housed more than a family and attendants. So the rolling plains and dark forests of Jotunheim were renowned among the Aesir as the choice location in all of the Nine Realms to find wild and fierce game.
In the far East of Jotunheim, broadly across from Asgard and closest in distance to Vanaheim, stood the citadel of Utgard. The largest single structure in the realm and the centerpiece of Jotunn military might; this enchanted citadel forced grudging respect out of even the most brusque of the gods.
One of the oldest stories of the Gods, said by some of the skalds to be the reason that the Aesir first ventured into Jotunheim, is that of a paradise for the gods residing in the lands beyond Asgard. The Jotnar have always claimed to know the whereabouts of its existence in Jotunheim but most of the Aesir have treated this as nothing more than boasting.
The Jotnar (Often translated into English as Giants, or Titans) are the most longstanding enemies and rivals of the Gods of Asgard. Though classically described as towering, man-eating monstrosities, the Aesir describe them as being as varied as the people of Midgard and that some could easily pass through a crowd of humans unobserved.
The gods also remember the Jotnar as being a solitary sort, mostly content with living in small family groups and surrounded by nature at its most untamed. They were only likely to gather for important events such as marriages, or when involved in one of their many wars with the Aesir.
“I have seen the summits of the Outlands, over the crests of the mountains that separate us and the Jotnar. And I see towers, spires, domes, and roosts: more than have ever existed in Jotunheim. I do not know how this has happened; not even Thrymheim stood as tall or as broad. But I know it to be true.”
- Frigg, relating a vision to the greater gods.
“The Jotunn King Thrym stood atop his mountain, watching the band of Aesir making their way towards his home. At the head of this party was, or so the Giant King thought, the daughter of Njord in beautiful wedding gown, and her bridesmaid riding beside. In truth, where the bridesmaid should ride sat the god of trickery, Loki. And in place of Freyja, resplendent in veil and gown, was the Son of Odin, Thor.
And as the sun rose, and night died, this unusual party from Asgard rode into Thrym's mountain home. Inside all was prepared, and a great feast laid out for to celebrate the marriage of the Jotunn King and Freyja. Thor searched all around but did not move nor speak, as the wedding dowry (the price for fair Freyja's hand) was the Thunder God's stolen hammer, Mjolnir.
When the evening came, and Thrym returned to the hall, mead and food was brought out for the Gods. As if unwatched, Sif's mate drank three tonnes of mead, a full ox, and eight salmon alone. Thus Thrym turned and said 'I have never seen a bride with such an appetite, and such a thirst for mead!' And the Trickster, sitting to Thor's left, replied 'Frejya has not slept for eight days, such was her longing for Jotunheim.'
At the time when the marriage was to be confirmed, Thrym, King of all Giants, called out for the hammer of Thor. And so he laid Mjolnir on Freyja's lap, as a blessing of their union. With eyes of fire, and a soul of stone, a hearty laugh left the Thor's mouth as he tore down his veil and took up his hammer.
Raising Mjolnir high above his head, he struck down the Jotunn King Thrym, and all of his kin. Returning to Asgard, hammer in hand, and God of Mischief safely in tow: he left no Jotnar alive that day. All of Thrym's family perished except his son Bergfinnr, who was unknown to the Aesir, and could not attend the ceremony.”