Limestone caves take millions of years to form.  It is made of prehistoric ocean life that died, hardened, and formed together with other fossils of huge sizes.  They struggle by the movement of the earths plates pushing them up onto the land.  They die by the movement of the earths plate because of the small tremors that we can sometimes not feel.  These caves are always wet, and a lot of the time there are streams running through, around, and under the cave.   You can tell when the caves gets cold ,when the cave gets dusty and when the formations begin to crumble.  Then the roof starts getting thin.  Then all of a sudden, the entire cave falls down only leaving a deep valley  or a big hole to mark its many years of growth.