Witness as the earth’s surface opens, revealing the entrance to Son Doong Cave. Roping up, prepare to commence an expedition in which you will climb up, rappel down, and scramble across this undulating subterranean landscape. Over the next four days, you will conquer the world’s biggest natural cave, so large that its own ecosystem has formed right inside. Prepare for an incredible sensory experience, as you adjust to the extreme stillness that comes from being cut off from the world above. Watch as slivers of natural light pierce the darkness, illuminating huge stalactites, stalagmites, cave pearls, and underground rivers.