of Puma Punku,

high in the Altaplano of Bolivia.

It's made out of gigantic blocks of sandstone and granite.

Some of them are weighing over a hundred tons.

Many of the granite blocks are finely articulated,

as if they were made by precision power tools.

Archaeologists are baffled by this structure.

They don't know what was here,

or what the purpose of Puma Punku originally was.

BRIEN FOERSTER: Puma Punku is unique

in terms of its construction.

Nowhere on Earth do we see the same style

of cutting into the stone

and the same obvious use of highly precision tools

in the distant past.

That's what makes it so mysterious.

Not only do these granite blocks have precision corners,

but they also have these difficult drill holes

that are going right through the rock.

Whatever kind of drilling mechanism they're using here

has to penetrate this very hard granite.

FOERSTER: It's an astonishing piece of work, and how anyone could think

that primitive human beings could have done this...

GIORGIO TSOUKALOS: In Puma Punku, the stone seems vitrified, too.

It is so smooth, it's as if you touch a bathroom mirror.

That's how perfect it is.

The so-called "H-blocks" are, in fact, shaped like dovetails

where there were clear deviations

in the width between the front and the back.

And possibly, they held something in place.

The question is, what?

FOERSTER: The great mystery

about Puma Punku is that the local people,

the Aymara, have only lived there for 900 years,

so they have no idea of who made Puma Punku and when.

The Inca also didn't know.

No one, in fact, on Earth knows

who built Puma Punku

and how far back in time it was first constructed.

That's the great mystery.

TSOUKALOS: Of all the ancient sites

we can find around the world,

I think that Puma Punku is the only one

that was actually built by extraterrestrials.

And perhaps these extraterrestrials knew

that some time in the future

another generation would stumble across this and wonder

how was such a thing even possible,

forcing us to acknowledge their existence in the remote past.

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