Here's a handy mnemonic for earth science. Mineral deposition creates both stalagmites and stalagmites, which are cave features. The first dangles, while the second ascends. To put it another way, a stalactite clings to a cave's roof, whereas a stalagmite may brush up against it.

A stalagmite in a remote Vietnamese cave could grow to be over 246 feet (75 metres) tall. That's quite cool.

Hang Sn ong is the name of the cave we're talking about. It's roughly 5.5 miles (8.8 kilometres) long and is located in Vietnam's Phong Nha – K Bàng National Park. As a result, Hang Sn oon is one of the world's largest caves.

There's a particularly long passage within this subterranean realm, measuring little under 4 miles (6.5 kilometres). The American Geophysical Union (AGU) published a report in 2011 describing "continuous widths" of roughly 328 feet (100 metres) inside. From floor to ceiling, the yawning hollow reaches a height of over 656 feet (200 metres).

Hang Sn ong is not only massive in size, but it also has a startling quantity of species.

Ho Khanh, a local, found the cave in 1990 and led the first expedition to sketch it out in 2009. Anyone with an internet connection may now "see" the geologic wonder for themselves; go to National Geographic's official website for a virtual 360-degree tour. You don't have a passport? It's no problem.

If you take this virtual tour – or a physical visit – you will undoubtedly discover two massive holes in Hang Sn ong's roof. Dolines are areas where the cave's ceiling collapsed due to its inability to support its own weight.

Trees, bushes, and other vegetation have thrived on Hang Sn ong's floor as a result of the openings, producing a subterranean habitat reminiscent of Jules Verne's science fiction masterpiece "Journey to the Center of the Earth."

A forested area beneath the cave's first main doline is known as "Watch Out for Dinosaurs" due to its prehistoric aspect.

The vegetation is home to monkeys, birds, and snakes, among other (non-extinct) species. You won't find any Velociraptor down there, unfortunately. If you're looking for prehistoric corals from the Carboniferous period, which existed between 359 and 299 million years ago, the remains of prehistoric corals have been discovered near "Watch Out for Dinosaurs."

The second big doline, roughly 535 feet (163 metres) across, is larger than the first. Another small jungle in the bowels of Hang Sn ong, dubbed the "Garden of Edam," receives its light from it. Native plants have colonised a rock pile left behind after the cave ceiling collapsed, and the greenery stands tall.

Hang Sn ong is thought to be between two and five million years old, according to geologists. This cave was carved out of the earth by ancient river water, and it still has a powerful river running through it.