Hang Son Doong Cave, Vietnam
Photo Credit: Joint British-Vietnamese Caving Expedition 2009 / Barcroft Media / Getty Images
In April 2009, a British Caving team believed that they discovered the biggest cave passage in the world. It is over 650 feet tall and 500 feet wide. It stretches two and a half miles. The reason it took so long to find it is because it is hidden by the tropical rainforest inside of the Phong Nha-Ke Bang National Park.
While from above, it may seem like a quiet cave, below, the Rao Thuong River courses through it, still eroding at the limestone within. Inside of the cave, several areas have collapsed, creating 100-foot natural skylights which contain their own ecosystems.
