SUBSCRIBE NOW HERE: / @coremystery-u4i Deep in Vietnam's Phong Nha-Ke Bang National Park, explorers have delved deeper into Son Doong, the world's largest cave, revealing chambers so vast they host their own microclimate and thriving rainforest 200 meters underground. Sunlight pierces through massive dolines, fueling ancient ecosystems with unique species, towering speleothems, and rivers that carve through time. This 2-5 million-year-old wonder, expanded by UNESCO in 2025, challenges our understanding of hidden worlds right beneath our feet.