Explorers who lowered themselves into a Vietnamese cave found a passage so vast it holds its own jungle, its own river and its own weather, a hidden world large enough to swallow a skyscraper - Space Daily

In the early 1990s, H Khanh found a dark opening while moving through the forest of central Vietnam. Wind pushed out of it. Somewhere below, water roared. The entrance dropped too steeply for him to … [+5683 chars]