It’s been there for Millions of Years, and we never even noticed it!!
A real underground kingdom.
In 1991, a simple farmer stumbled across a previously unexplored cave in Phon Nha-Ke Bang national park, Vietnam. A terrible roar of water emanated from the entrance, frightening him, and he decided not to go inside. The local inhabitants named the cave Son Doong, but none of them dared to explore it.

It was only in 2009 that a group of British scientists led by Howard Limbert, having once again located the cave, decided to go inside. What they found was an entirely self-contained world, five kilometres long and 150 metres wide. Having explored it, they were able to confirm that Son Doong is in fact the largest cave on the planet.