Turquoise Ice, Lake Baikal, Russia
Lake Baikal is the largest and oldest freshwater lake in the world. In the winter, the lake freezes, but the water is so clear that you can see 130 feet below the ice. In March, frost and sun cause cracks in the ice crust, which results in the turquoise ice shards we see at the surface.
Sadly, the mining company that owns the caves could no longer afford to keep the massive pumps going to clear the chamber. I believe the pumps were shut down a few years ago and the cavern is refilled with water. The crystals are growing once again, but no one will ever see it.