Phong Nha cave and Dark cave tour of Phong Nha Locals will be the unforgetable memory for your travelling. Phong Nha cave and dark cave tour is the process of going to the cave called the cave dark because it is made mostly of limestone basalt outside. The basalt is a black hard rock, giving it its dark name. Basalt and limestone surrounds you, you crush the entire paragraph just use your head lights. By the time we got through the passage, you are covered in mud and ready for another swim. This time you can go further into the cave. Where the width was probably 100m and the depth is deeper than anyone could touch. As you swim, you have to duck under huge stalagmites. And balance between limestone columns to get to the next big opening.