Generally one thinks of the oceans and space as being the final frontiers of exploration. Most people forget about the unforgettable experience found in the exploration of natures mysterious underground world of caves.
Caves are natural openings within the earth large enough for a person to enter.
They gradually extend beyond the reach of the light from the surface area. Cave is used to describe one underground room. When caves contain connecting rooms, they are called caverns. People tend to think of caves as barren, lifeless areas. This could not be farther from the truth.