According to the Business Insider, Hang Son Doong (or the Son Doong Cave), which is classified as the largest cave in the world, can be found in the Quang Bình province of Vietnam. It has a width of about 300 feet (150 meters), a height of 330 feet (200 meters), and a length of more than 6,000 feet (5 kilometers). It has huge skylights and caverns that are big enough to hold entire city streets.

Some of the 24 incredible underground attractions include the Salt Cathedral of Zipaquira in Colombia; Salina Turda in Turda, Romania; St. Michael’s Cave in the Upper Rock Nature Reserve of Gibraltar; Bounce Below in Blaenau Ffestiniog, North Wales; Zip World Caverns in Gwynedd; Bluegrass Underground in McMinnville, Tennessee; the Waitomo Glowworm Caves of Waitomo, on the North Island of New Zealand; the Postojna Cave in Postojna, Slovenia...

By Nhu Y
(Source: Business Insider)