Mysterious cave and grottos

"According to geologists, Vietnam has limestone groups which formed during the Mid-Cambri to Mid-Dev eras (about 500-520 million years ago).
Their formation created cave and grottos, which are from dozen to hundreds of metres deep and have simple and complicated compositions.
Examples are the Cong Nuoc Cave in Tam Duong, Lai Chau Province, 602m deep and the Phong Nha-Ke Bang system of caves and grottos in Quang Binh Province, several dozens of metres long.
Many big rocks have limestone artesian water running inside, creating gigantic underground rivers. The calcium precipitates (CaC03) in the caves and grottos create stalactites and stalagmites looking like bells, curtains, screens and pillars.
The Phong Nha system of caves and grottos has a total length of more than 40km. Phong Nha Cave alone is 7.7km long and consists of 14 separate caves created by limestone-dissolved underground rivers. In some places, the caves are connected and are above and below ground.
The limestone mountainous areas also have a unique and diverse ecological system with rare and precious fauna and flora. Now that the natural preservation and environmental protection have become important issues, these areas provide an opportunity to achieve a harmony between development and preservation.(...)"

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