Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum.
(Image sours: https://en.wikipedia.org/wiki/Karst)
The Karst towers are formed when the roof of a cave collapses or simply are eroded away over a loong time by wind, water, or other natural agents and gradually wear away.
As a result of this, the columns in the original cave are all that is left from the cave, and they become a part of the open landscape.
When this happend with gigantic cave systems, we are left with amazing landscape as we can see on this picture with a lot of Karst towers that look like mountains.
(image sourse: http://science-junkie.tumblr.com/post/42590142332/tower-karst-tower-karst-is-a-spectacular-variety)