But nobody knew any of that until about six years ago.
The recently discovered cave has been touted as the largest in the world, although other caves vie for the title of longest (Mammoth Cave in Brownsville, Kentucky nabs that title with about 400 miles of passageways) and deepest (Krubera Cave in the nation of Georgia).
The lucky people who have entered Son Doong so far, like photographer John Spies, have emerged with some amazing photos.
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Fields of algae from ancient pools blanket parts of the cave's interior.
Son Doong is a jackpot of rare cave pearls. The pearls form over hundreds of years as water drips down, dries up and leaves layers of calcite crystals on grains of sand.
Scientists have discovered never-before-seen plant species around Son Doong's waterfalls. Oh, and there's a whole river in there, too.
Can't shell out thousands of dollars for a tour? Take this virtual journey into Son Doong's forests!
This post has been updated with additional context on other superlative cave systems.
Photos by John Spies and Carsten Peters/Getty Images.