Chillagoe Caves

The limestone at Chillagoe is Devonian, about 400 million years old and far older than most limestone deposits. It's formed from shells, primitive Rugose corals and crinoids, and when fresh is a blueish colour. The caves themselves are far younger, but still probably several million years old. The stalactites and stalagmites grow slowly in a dry climate, and many are several metres long.

Three caves are open for guided tours, and I visited all three over two days. Lots of opportunities for playing with long exposure photography!