When I was in Tassie recently I visited the Marakoopa caves, located on the slopes of the Great Western Tiers. From memory they're around 300 million years old. The caves are part of an internationally significant karst system and are in a National Park. To visit them you have to do a tour and dress warmly - it's always 9˚C in there.
There are two streams in the cave and a variety of geological structures including stalagmites, stalactites, straws, curtains and flow stones. Water in the cave runs along the limestone, collecting calcium which is deposited on the surface. When it is wet, it glistens and glitters; sparkling in the light from a torch.
Our guide pointed out a stalagmite and a stalactite which were about ten centimetres apart. He told us it would be a hundred thousand years or so before they joined up. The straws in the cave on the other hand, grow quite quickly. They only take abut ten thousand years or so to grow. Time moves slowly when you're a rock!
The water in the cave is pure and clear. At one stage John, our guide, pointed to a shallow depression in the ground surrounded by formations known as lilies. The reason for their name will become apparent in a sec. There was water in the depression which we couldn't see at first because it was so clear. If he hadn't pointed it out, I wouldn't have know there was a pool there. It's incredible to think that all our water used to be so pristine.
As well as the stunning rock formations I also saw a spindly, long legged cave spider on the roof near the entrance. I'm not a huge fan of spiders so I didn't try to get close enough to take a photo.
At the end of the tour, our guide turned off the electric lights and the ceiling began to flicker with the lights from the minute glow worms living on the ceiling above the water. Glow worms are only found in Australia and New Zealand. A chemical reaction in their abdominal malpighian tubes creates the light. They live ten to fifteen years as teenaged larvae, creating a cosmos on the ceiling, feeding on mosquitoes that breed in the water below. Once they hatch into a fly they mate and only live for 2-3 days before dying without eating.
Being in the caves felt like being in another world. The air is still and cold. All the sounds of insects, animals and birds are gone. It is quiet except for the sound of water. It's easy to loose all sense of time and place when you're deep in the earth.