John Hopkins

With its warfare mechanized in a way the world had not yet known was possible, it foreshadowed the horrors of the Second World War, with terrifying bombing campaigns unleashed against innocent populations, and civilians drawn into the conflict as much as frontline soldiers.

It prefigured the intense ideological contests between communism and fascism that marked much of the 20th century, and its cultural and symbolic impacts echo even today, almost a century later.

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It's Thursday, October the 28th, 2004.

In South Africa, the undulating plains of the Kalahari Desert stretch out beneath a pale sky, the ochre-colored earth and scrub brush warmed by the brilliant sunshine.

But in an isolated corner of the country's northern Cape province, this vast rolling expanse is suddenly interrupted, punctured by an enormous sinkhole, as if a titan's fist has punched through the landscape, leaving a deep, gaping wound in the ground.

The walls of the abyss plunge down towards a small, duckweed-covered pond below.

At first sight, there is nothing remarkable about it.

But beneath the surface, this pool opens up into a spectacular bell-shaped chamber, a submerged natural cathedral.

This is Bushman's Hole, one of the largest freshwater caves in the world.

Nobody is entirely sure how deep it may go.

No light or sound penetrates its depths.

It is an inhospitable alien place, a dead zone.

And yet today, life has come to Bushmans.

Deep below the surface, a tiny pinprick of light descends steadily through the infinite darkness.

It's a torch belonging to 50-year-old diver Dave Shaw.

He glides gracefully downwards with single-minded focus, guided by a weighted shot line.

At around 260 meters, or 850 feet, Dave reaches the silty, sloping bottom of the chamber.

Dave pushes deeper into the unknown, keen to explore the uncharted floor of the cave.