If anything proves we don't know what's lurking under the ground we walk on, it's the in Guilin, China. It was discovered in modern times by a group of people fleeing Japanese forces during World War II in the 1940s and looking for refuge.
Inside the 787-foot-long cave is proof these refugees weren't the first people to stumble upon this shelter. You see, there are ink writings on the stone that scientists believe are from 792 CE, during the time of the Tang dynasty. But the limestone cave existed long before that too, as it's believed to be over 180 million years old. Talk about a complicated timeline.
Today, visitors from all over the world flock to this natural wonder, which was named after the reeds that grow at the entrance to the cave and are used to make flutes and other wind instruments. Inside, the cave is lit up by colorful lights, which turns some of Mother Nature's most impressive work into an elaborate and exciting art show.
Take a look: