Son Doong cave is world’s largest cave, located in Quang Binh province, Vietnam. As strange as it sounds,  no one knew it was the largest until British explorers first explored its depths in 2009. The Vietnamese cave was discovered by local man Ho Khanh in 1991, but he could not descend into the cave. The British expedition uncovered incredible natural wonders within the cave, like towering stalagmites, rare cave pearls, a river, underground jungle ecosystems, cave-dwelling species, a cloud system within the open taverns, and ancient fossils. Some caverns of the cave, which is 9km long, 200km wide and 150km tall, can fit entire skyscrapers or city blocks. Source: National Geographic | Photographer: Carsten Peter