The Seduction of Svadilfari
This story more or less directly follows the action of chapter 43 of Gylfaginning, part of the collection of Norse myths known as the Prose Edda, my version is slightly expanded, however, and in particular the mating of Loki and Svadilfari is depicted explicitly (albeit briefly), rather than merely being alluded to.
On one autumn day at the dawn of time, when Asgard was new, a lone traveler rode in one day and approached the gods with an offer.
"O lords of the Aesir and Vanir, your might is great, but so is that of your enemies the frost and fire giants. If you will accept my price then I will build you a stronghold impenetrable to all harm"
Wotan the Allfather replied, inquiring "What price do you ask for this task?"
"I seek only the hand in marriage of the Lady of the Slain, the great goddess Freyja" said the traveler
"Before we even consider this, I wish to make sure that you speak truly and there is no additional expense you expect to make us pay as well. Where do you intend to house your workers? and how do you intend to pay them? Shall we be expected to feed and house all of them during the years of construction?"
"I have no workers but myself and my workhorse Svadilfari," he replied, gesturing at the black stallion, "and if we start without delay, our work will be complete before the spring's end"
Here Freyja spoke up "If you can truly do all the miraculous things that you say then I would be happy to be your wife"
"Ha!" laughed Loki, the god of mischief, "If you can do all that, we'll throw in the sun and the moon as well!"
"I will hold you to that son of Laufey"
Unthinkable though it had seemed, work on the fortress progressed at an epic pace. The stranger, with little effort, could lift solid stones as big as himself and hammer in nails with his hands, and the workhorse Svadilfari had to be weighed down with a burden that would completely immobilize a small team of normal horses simply to be slowed to the speed of an ordinary unburdened charger; he hauled in stones as big as houses for his master to use in the construction.
As fall turned to winter and winter turned into spring, the work of building the fortress drew close to completion.
Wotan's scouts, the ravens Hugin and Munin, returned one late spring day from their daily survey of the world.
"The stranger's work continues at the same great pace as it has been my lord," reported Munin
"This is distressing," added Hugin, "At this rate he will be done days ahead of schedule"
"Loki promised him the sun and the moon should he succeed," declared Munin, "we cannot afford to lose them!"
"Loki should be the one who should bear the brunt of fixing this," concluded Hugin.
Later that day, a council of the gods was convened, and it was agreed that Loki should fix the situation or face the wrath of his fellow gods and goddesses for gambling away their claim to the celestial orbs.
Observing that work on the fortress could not progress at nearly its lightning pace without the stallion Svadilfari Loki devised a devious plan whereby the progress of construction would be disrupted for the few remaining days until the beginning of summer.
Shortly before dawn, as work was about to recommence, a comely and fragrant mare passed by the construction site as Svadilfari was about to be harnessed.
Her coat was a brilliant white, and seemingly untouched by the mud and the dirt, her teeth as perfect as those of a newborn foal, and the scent of her heat more alluring than any other mare in all of the nine worlds. She lifted her tail and exposed her perfectly formed vulva, beckoning to Svadilfari.
Confronted by this beauty, Svadilfari bolted from his handler to embrace the mare. The mare, however, did not intend to surrender her treasure impetuously, for she was actually Loki in an alternate shape, and her primary concern was to keep the mighty stallion from continuing his work. She dashed off into the forest and the Svadilfari gave chase. The builder hurriedly chased after them but Loki and Svadilfari were too swift and he was powerless to keep up.
If ever Svadilfari lagged behind, Loki lifted her tail again to remind him of the priceless jewel he was pursuing. Loki ran, leading Svadilfari, until she was sure that they had left the builder far behind and stopped to rest in a small clearing. It was here that she first surrendered her prize to Svadilfari.
The great stallion tenderly nudged Loki and sniffed at her pudenda. Svadilfari's formidable tool emerged from his sheath, greater than any tool in his master's retinue and as mighty as the rest of the stallion. Climbing upon Loki, he slid his great erection between her folds, occupying her passage completely. Svadilfari began thrusting, keeping up a swift steady pace which quickly gratified Loki, and later brought about his own climax, spewing his potent seed in quantities worthy of such a mighty creature, filling Loki's fertile womb.
Over the following hours the two coupled further, but it was not to last, Loki heard the builder approaching and led Svadilfari further into the forest. When next they rested, Loki accepted Svadilfari's seed once more, but again led Svadilfari away when she heard the builder once more approach, and things continued in this way for quite a long time.
Finally, in furious desperation to find and catch his workhorse, the builder grew to enormous size, towering above the trees and covering the land in great strides. Upon seeing this the gods knew that he was a spy for the race of giants, and likely a saboteur as well. The gods went to examine the fortress, and what had fooled the ravens Hugin and Munin could not fool the Wise One, the Lord of the Aesir. Part of the castle's walls had been constructed from flimsy wooden boards, as might be easily removed even by mere human invaders, and disguised with sorcery to look like stone.
Enraged at this treachery, Wotan called for Thor, the Thunderer, and appraised him of the situation. Thor took up his mighty hammer Mjolnir and set out to slay the giant. The giant was mighty, but Thor's might was greater and his skill with his hammer unmatched, With a single blow he struck down the giant and cracked his skull in twain.
The gods completed construction on the castle themselves and fortified the false wall, but throughout the process Loki was absent. Two years went by, and the gods were beginning to believe that the trickster was gone or good, until one day Loki appeared amongst the gods, once more in his humanoid form, riding upon the builder's horse and leading an eight legged gray colt. He dismounted and led the eight legged colt to Wotan.
"We meet again blood-brother. This is Sleipnir, my son, in time he will surely make a mighty steed. I leave him in your care. Don't say I never gave you anything."
He then departed, leaving the assembled gods to discuss the implications bewilderedly amongst themselves.
Notes:
This story is based heavily on the forty-third chapter of the "Gylfaginning" section of the Prose Edda. I highly recommend that you check it out for yourself (http://en.wikisource.org/wiki/Prose_Edda/Gylfaginning)