Waitomo Glowworm Caves, Waitomo, North Island, New Zealand

Geological and volcanic activity has created around 300 known limestone caves in the Waitomo region over the last 30 million years.
The limestone formations in the Waitomo Glowworm Caves were formed when the region was still under the ocean about 30 million years ago. The limestone is composed of fossilized corals, sea shells, fish skeletons, and many small marine organisms on the sea beds. Over millions of years, these fossilized rocks have been layered upon each other and compressed to create limestone and within the Waitomo region the limestone can be over 200 m thick.
The caves began to form when earth movement caused the hard limestone to bend and buckle under the ocean and rise above the sea floor. As the rock was exposed to air, it separated and created cracks and weaknesses that allowed for water to flow through them dissolving the limestone and over millions of years large caves were formed.
The stalactites, stalagmites, and other cave formations grew from water dripping from the ceiling or flowing over the walls and leaving behind limestone deposits. The stalagmites form upward from the floor while the stalactites form from the ceiling. When these formations connect they are called pillars or columns and if they twist around each other they are called helicti. These cave decorations take millions of years to form given that the average stalactite grows one cubic centimetre every 100 years.