The World's largest cave (Song dong cave)

A man accidentally discovered a giant hole in a huge mountain then the whole world surprised. 

Vietnam's Son Dong Cave is the world's most beautiful and largest cave. If you visit once, it will be a great experience for you. It also has massive space the same as a 40 floors building. 

The word "son dong cave" means "mountain river cave". This was first discovered by a farmer in 1991 years.