So twenty years ago Vietnam’s Hang Son Doong cave was discovered. It is the largest in the world, with quite possibly the biggest subterranean passage on the planet, capable of fitting inside a half-mile block of 40-story buildings. You can get a pretty good idea of the scale with the first picture of the lone explorer in the center. The cave also has its own jungle.
"This tiny jungle, nicknamed the "Garden of Edam", formed underneath a collapsed roof of the cave, which allowed first light and then vegetation to make its way inside the cave. It’s very possible that this is the largest jungle inside a cave in the entire world."
For whatever reason, the cave was properly surveyed earlier this year. National Geographic has a fascinating longer piece on the recent explorations of the cave, and also an amazing gallery of around two dozen images.