Hel.

A hall I saw, far from the sun,

On Nastrond it stands, and the doors face north,

Venom drops through the smoke-vent down,

For around the walls do serpents wind.

I saw there wading through rivers wild

Treacherous men and murderers too,

And workers of ill with the wives of men;

There Nithhogg sucked the blood of the slain,

And the wolf tore men; would you know yet more?

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It's probably a mistake, but I think of the Vikings as being just about as close as I can get to any written record of an Iron Age way of life and thinking.

On their incredibly long journeys and through their extensive trade networks came both  physical objects and intangible ideas from cities far away, both in space and sophistication. The Vikings crossed seas and followed rivers inland, down the great rivers of Russia to the  Caspian and the Black Sea, through the Straits of Gibraltar and over the Mediterranean; across the Atlantic to the Faroes, Iceland, Greenland and on to America.

Better still, they were written about and their poems were preserved.

The Poetic, or Elder Edda.
Norse myth was collected and written down: The Codex Regius was written around the year 1270  in Iceland from an original compilation (now lost) thought to have been made in 1225. It contains the Elder Edda- a collection of 39 poems. The poems are older than the book and were a mixture of stories and advice.

The Prose Edda.
http://www.gutenberg.org/files/14726/14726-h/14726-h.htm
Written by the Icelandic scholar and historian Snorri Sturluson from the Poetic Edda. It could be described as the handbook to accompany the Poetic Edda. The Prose Edda is a compilation of stories from the Poetic Edda to provide a connected, systematic account of Norse cosmology.

What of Hel?
The Vikings describe a triple level world; a realm of the gods, a middle earth (where we live) and an underworld. Hel is the Queen of the underworld, the custodian of those who die of old age or before their time, and of cowards and criminals.

Hel resides over a place of punishment for those who deserve it. But her world is not Hell for those who do not deserve punishment- the old and the young.

From the battlefield, with Odin go the brave to Valholl , the good go with Fraya to the Fólkvangr...

Fólkvangr 't is called, where Freyja rules
    Degrees of seats in the hall;
Half the kill she keepeth each day,
    And half Odin hath.

and the rest...sink to Hel to be judged.

As in Greek myth, the underworld has levels deeper than death, the lowest space is filled with mist:

To the nine worlds I came
To Niflhel beneath
Where the dead from Hel descend.
From: Vafþrúðnismál 

The greatest of all is this: that he made man, and gave him the spirit, which shall live and never perish, though the flesh-frame rot to mould, or burn to ashes; and all men shall live, such as are just in action, and be with himself in the place called Gimlé (after Ragnarok, the new world). But evil men go to Hel and thence down to the Misty Hel; and that is down in the ninth world."
From: Gylfaginning. 

As is clear from the last quote, the idea ofthe soul and the last battle, refuses to stay inside Christianity.

Snorri describes Hel  in the second part of his Prose Edda, Gylfaginning:
Loki, trickster god and Angrboda (Bringer of distress) a giantess in Jötunheim, had three children: one was Fenris-Wolf, the second Jörmungandr--that is the Midgard Serpent,--the third is Hel.

Odin threw the serpent into the deep sea, where he lies about all the land; and this serpent grew so greatly that he lies in the midst of the ocean encompassing all the land, and bites upon his own tail.

Hel he cast into Niflheim, and gave to her power over nine worlds, to apportion all abodes among those that were sent to her: that is, men dead of sickness or of old age. She has great possessions there; her walls are exceeding high and her gates great. Her hall is called Sleet-Cold; her dish, Hunger; Famine is her knife; Idler, her thrall; Sloven, her maidservant; Pit of Stumbling, her threshold, by which one enters; Disease, her bed; Gleaming Bale, her bed-hangings. She is half blue-black and half flesh-color (by which she is easily recognized), and very lowering and fierce.

The Wolf the Æsir brought up at home, and Týr alone dared go to him to give him meat.

The Gylfaginning contains the story of Hermódr's ride to the underworld to try to restore Balder back to life.

The road the dead have to take- the Helway - leads northwards and down. Its entrance is a cave guarded by Garm, a warg-hound with a blood smeared chest. The dead do not dance following a bright god like Dionysos, instead they trudge for days over mountains and through dark forests and down into bleak valleys. The Helway ends in a place of of noise and confusion,  at an 'ice-wave' the river of blades. This river rises from the coldest and deepest part of the underworld. It name is Gjöll (resounding). It is impossible to cross Gjöll in a boat or to swim; it is a river so cold, as if of liquid nitrogen and full of razor sharp knives flowing through it.

Hermódr's ride on Sleipnir took nine nights and nine days to reach this place.

The river of blades is crossed by a bridge thatched with glittering gold. Módgudr (or Móðgunnur) is the woman who guards the bridge...

The blades, the bridge and the girl are themes found in Zoroastrean texts. 
The Chinvat bridge may be as narrow as a hair, or as broad as a road. For the bad, a demon called Vizaresh would emerge and drag the soul into the druj-demana (the House of Lies), a place of eternal punishment and suffering similar to the familiar concept of Hell. However, if a person's good thoughts, words and deeds in life were many, the bridge would be wide enough to cross, and the Daena, a spirit representing revelation, would appear and lead the soul into the House of Song...

The bridges in Muslim belief cross fire:

As-Sirāt al-Mustaqeem is the straight path over hell, a fire more intense in heat than boiling molten brass, and it has seven bridges over it: Each is three thousand years in length: one thousand to vertically ascend, one thousand to horizontally cross, and one thousand to descend. It is thinner than a human hair, sharper than the sharpest sword and darker than the darkest night inside a tunnel. Each bridge has seven branches, and each branch is like a long lance with sharp teeth: each servant of Allāh will be confined on each and every one of them and be asked about all the injunctions the Almighty had required him to perform during his lifetime on this planet....continue.

After the bridge Hermód sees the walls of Hel's land. Sleipnir jumps them easily.

Where is Hel?

In the song of the sun Sólarljóð the poet seems to say that the Hel-gate is in the east- opposite the setting sun:

The sun I saw,
true star of day,
sink in its roaring home;
but Hel's grated doors
on the other side I heard
heavily creaking.
And, as in Gylfaginning, the river Gjöll runs nearby:

The sun I saw:
she beamed forth so
that I seemed nothing to know;
but Giöll's streams
roared from the other side
mingled much with blood...

So a north east direction for the mouth of a tomb would make sense..specifically winter time...
From the September equinox until the march equinox, the sun sets in the southwest quadrant- so the Hel-gate is north east....

More sun and moon facts:

At the winter solstice in the Northern Hemisphere the Sun's annual path across the sky is at its lowest, or closest to the southern horizon, while the Moon's path is at its highest north.

The Sun and Moon appear to reverse positions at the summer solstice with the Sun at its highest north and the Moon at it's lowest south.