What is being hailed as the 'Eighth Wonder of the World' was discovered in the crack of a mountain, marking a truly sensational discovery.

While many of us are familiar of the seven wonders of the world; Colossus of Rhodes, Great Pyramid of Giza, Hanging Gardens of Babylon, Statue of Zeus at Olympia, Temple of Artemis at Ephesus, Mausoleum at Halicarnassus, and Lighthouse of Alexandria - it's seems there may be another one we ought to add to the list.

The wonder in question, a nearly nine-kilometre-spanning underground kingdom, lies buried deep in the jungle of central Vietnam.

Known as Son Doong, which translates to English as 'mountain river cave', is the largest cave passage in the entire world.

Not just heralded for its sheer grandeur - the underground cave is also a place of outstanding natural beauty complete with its very own weather system, a jungle, multiple lakes and peaks tall enough to fit New York City skyscrapers inside - granted they're 40-stories of less given its tremendous 200 metre height.

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The cave - believed to be between two and five million years old - can be found in the Phong Nha-Ke Bang National Park in Quang Binh Province and was only discovered a few decades back in 1991 by a local farmer.

However, it was only officially explored nearly 20 years after its first discovery in 2009 when the British Cave Research Association descended into it.

Since then, more people have reportedly summited the mammoth Mount Everest than have been through Hang Son Doong.

While the natural phenomenon lay undisturbed more million of years - its future became a point of issue after plans were considered to build a cable car through the cave back in 2014.

However, such plans for development were later thwarted by environmentalists and locals alike due to the damage mass tourism could do to the area and fragile eco-system yet many were still left divided over potential benefits it could bring.

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Now, in a relatively recent documentary - first released in the UK and Ireland a couple months back (26 May) - people can get a closer look inside the marvel and how the local community fared as the events unfolded.

The award-winning feature length doc goes on to tell the story of the Son Doong cave and the fight to protect it.

The film in question, aptly titled A Crack in the Mountain, is currently available to watch on Curzon.

"At its core, A Crack In The Mountain is a lens through which to explore the challenges which modern day Vietnam faces," director Alastair Evans said.

"As the clock ticks down and people around the world struggle to find that optimum balance point between environmental sustainability and economic growth, nowhere is this battle more keenly contested than in a rapidly developing nation such as Vietnam."