Three main rock forms are found in inland caves: columns, stalactites, and stalagmites. They are all created by the same process of erosion, only in reverse.
As the acidified rainwater cuts through the limestone, it retains limestone particles. When a drip from the ceiling of a cave falls constantly on the same spot, it leaves the limestone deposit behind.
Over time this builds up into a cone shape, much like if you let sand run through your fist, it forms a cone. The deposits collect on both the ceiling and the floor of the cave where the drops continue to fall.
The cones hanging from the ceiling are called stalactites. The cones that seem to grow from the ground are stalagmites.