The world map can be deceiving; it creates an illusion that there is nothing left on Earth to discover. But the depths of the ocean are still largely unexplored and some parts of the poles haven’t yet been seen by human eyes.
Slideshow: The Most Beautiful Caves in the World
Other than that it seems that people have found almost everything else—and this is where caves come in.
These structures are incredible feats of nature and man. Caves are formed by the dissolution of limestone. Rainwater picks up carbon dioxide from the air and it infiltrates the soil, which turns into a weak acid. This slowly softens out the limestone, bedding planes and fractures, some of which become enlarged enough to form caves.
Adventure travelers love to explore these odd and phenomenal natural formations – whether those made of ice, crystals, sea caves or those under volcanoes – for their colors, patterns, history, and cultural importance.
Though you may not be able to visit and get inside some of these caves, they are definitely worth a look.