Vietnam's Phong Nha-Ke Bàng National Park is home to world's largest cave that is visited by only few hundred tourists. It is called Hang Son Doong cave. It remained an less known place until 2014 when it was thoroughly explored, it was then when government allowed tourists visit this cave under supervision of special tour operators. Before visiting this cave, one must get a license from the government. So far, only few hundreds licenses have been issued. World's this largest cave is 5 km long, 200m high and 150m wide.
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