Mount Napier The caves were formed from lava flowing from the volcano crater cooling rapidly and forming a crust, while beneath it molten lava continued to flow. The eruption ceased, the lave flow continued on and the caves remained. As the eruption occurred relatively recently, the caves have not had time to erode and give an insight into the spectacular events of the past.
The largest caves are 18 metres wide, 10 metres high and extend 20 metres below the surface. At this time only one cave is open for public inspection, the Harmans 1 cave. It is important when entering the cave to wear appropriate footwear and to carry a torch with you. The cave is sometimes home to bats in winter and it is asked to not disturb them through noise or shining lights in their direction.