NARRATOR: County Meath, Ireland.
Rising above this region's lush fields,
not far from the banks of the River Boyne,
is one of the most mysterious ancient tools in the world--
Newgrange.
This massive stone structure has a diameter of 87 yards,
or nearly the size of a football field.
Newgrange is the envy of monuments
all around the planet.
The thing that people say when they come here
is they're surprised how big it is.
It is huge.
It takes up over an acre of ground.
And there is an estimated 200,000
tons of stone in the monument.
NARRATOR: According to archaeological findings,
Newgrange was built around the year 3200 BC,
making it centuries older than both Stonehenge
and the Great Pyramid in Egypt.
Because Newgrange is so ancient, there's still much
that we don't know about the people who
built this extraordinary tomb.
Probably one of the most fascinating things about
Newgrange is the fact that it was built in pre-metal days,
just as the Stone Age was sort of coming to a close.
And it's difficult to imagine how ancient people were
able to assemble this massive monument,
but they managed to do so.
A lot of work went into the building of this monument,
and it was all done with extreme precision.
Inside, there are carved stones.
And then you come into a chamber which is quite roomy.
So you have this cathedral-like feeling when you walk inside.
Newgrange is what archaeologists
refer to as a passage tomb.
It has a passage leading into the interior.
And in that interior, human bones have generally been
found in different quantities.
There are human remains in these places.
But the most common burial practice around this time
was cremation.
So we find most people would be cremated and then interned.
In the traditional Irish folklore that dates way,
way back, the other world of the dead,
it sort of overlapped with our own.
So the idea is that these sites would allow
for this passage between the realm of the dead
and the realm of the living.
On the back recess of the inner chamber,
there is a tri-spiral.
The most common interpretation that people come up with
is that it represents this constant cycle
of renewal and regeneration.
On a spiritual level, it may promise rebirth
for the spirits of the dead.
The tri-spiral is unique to Newgrange.
And it's also found on the entrance dome
and throughout the tomb.
NARRATOR: Archaeologists who have studied Newgrange have
theorized that this ancient tomb was
intended to serve a profound and mystical purpose.
And as evidence, they point to a curious element of its design
that is visible only one day a year.
Newgrange is unusual in that it has a very special aperture
or opening above the entrance.
On the day of winter solstice, this glimmering
golden beam of sunlight enters there and pierces the darkness.
When the sun rises at winter solstice,
the light hits the chamber for precisely 17 minutes.
And some even speculate that the spirits would have used
the light to leave the burial chamber
and go and join the deities.
NARRATOR: Did the builders of Newgrange
specifically design it to be a gateway into the afterlife?
Some archaeologists believe that the answer is yes.
And they also claim that Newgrange was built
to allow those who stood within its inner chamber
to communicate directly with the dead.
In the case of Newgrange, the notion of the sunbeam drawing
out the souls of the deceased and leading
them to that other world is not just a one-way ticket.
It was a portal between worlds.
Were the people inside there-- the priests,
for instance, the druids--
were they in contact with the ancestors who had gone before?
The builders of the monument have
created a space which is separate,
which is a world of the dead.
There is always a feeling that this
is the house for the spirits, where
consulting with the ancestors, asking advice
from the ancestors would have happened 5,000 years
ago, which is extraordinary.
NARRATOR: Was Newgrange constructed
to be not only a tomb but also a place where the living
communicated with the dead?
It's an intriguing theory, which is why archaeologists continue
to study Newgrange in the hope of one day unraveling
all of its mysteries.