Popular for being one of the largest caves in the world, Son Doong Cave in Vietnam is one of a kind, according to the website. Translating to “River Mountain Cave,” it is believed that the cave has been formed by river, Rao Thuong River erosion into the base of a limestone mountain, Truong Son. Hence, a large tunnel was formed underneath the tunnel. Being 200m high and 175m wide as well as 9.4km in length, this cave is estimated to fit a 40-story New York skyscraper, the website noted. The most fascinating elements are a thick forest mushrooming in the cave for years as well as towering stalagmites, phytokarst, cave pearls, as well as cave roof, collapses. It requires two days of intense jungle trekking and river crossings to reach the entrance of Son Doong Cave. The Travel also revealed that an expedition to the cave costs around 3,000 USD for four days via Phong Nha-Ke Bang National Park Management Board. Currently, tour activities are operated by Oxalis Adventure./.