Boxwork in Jewel Cave
Jewel Cave is currently the 3rd most extensive cave network in the world. It is believed to have formed completely underwater, thus leading to the extensive coating of calcite crystals.
This image shows a formation known as boxwork, which forms when dissolved calcium carbonate forms calcite crystals in cracks in rock formations. The surrounding rock formations eventually erode away, leaving the angular formations.
Although Jewel Cave's neighbor, Wind Cave, is more known for boxwork, Jewel Cave itself has plenty of boxwork.