In 1991, logger Ho Khanh stumbled upon a hidden entrance to a massive underground chamber in Quang Binh Province, Vietnam. Almost two decades later, the British Cave Research Association explored the cave and discovered an entire ecosystem inside. The Son Doong cave is estimated to be around 3 million years old, stretching through the Earth for nearly 6 miles, and containing an ancient forest and a flowing river.

According to local residents, strange reptilian-type humanoid beings live deep inside the cave, resembling the seraphim or winged serpents in Kabbalistic tradition, who are said to have lived in the inner Earth. Reports of reptilian beings have been found in underground caverns across the world, including during the Vietnam War when US soldiers claimed to have encountered upright lizards inhabiting caves.

Another inner Earth entity commonly witnessed in modern times is the black-eyed entities or Greys, who are often reported by alleged alien abductees. Many of these abductees claim to have been taken aboard saucer-shaped craft, leading some ancient astronaut theorists to suggest that flying saucers are not coming from outer space, but rather from inside the Earth, supported by numerous accounts of UFOs disappearing into the landscape and even flying directly into mountains.