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1. Hang Sơn Đoòng, Vietnam

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Where better to start than the world’s largest cave? Hang Sơn Đoòng, which translates as mountain river cave, is in Vietnam’s Phong Nha Ke Bang National Park. The main cavern alone is 650 feet high and three miles long, while the rest of the cave stretches on for nine miles in total. Ceiling collapses have let in light, and that’s allowed some impressive verdant foliage to come to life in its depths – a pretty unique phenomenon. It even has its own weather system, clouds included, and the largest stalagmite known to man.