The world’s largest cave, Hang Son Doong in central Vietnam’s Phong Nha-Ke Bang national park, was explored by scientists for the first time in 2009, after a local man, Ho Khanh, discovered it in 1991, but did not locate it again until many years later. Son Doong 360 is a project by National Geographic aiming to preserve the cave in digital form before it becomes subject to extensive tourism development. A trek – created from 360-degree images and atmospheric sound effects – heads through light-filled caverns, passing a 70 metre-tall stalagmite called Hand of Dog, and huge sinkhole jungles. Keep an eye out for members of the expedition crew, and take advantage of the high- definition images to zoom into details of the cave’s geology, flora – and fauna, too, if you look hard enough. The Grand Canyon, USA, and Everest in Nepal are also in the list./.