You can find photos of caves in this category since they are geological formation created by water flows inside the mountains. Thousands of years are necessary to make impressive stalactites and stalagmite: lime deposits of calcium carbonate or other stone make these column that are characterized by different colors and shapes. Many pictures are taken in the "Wind cave" settled on the border between Tuscany and Liguria. Colourful caves can be seen visiting the Ludi cave in China.
photo -> nature -> mountains -> cave