Cave formations often have a property called fluorescence due to impurities in the water that forms them. The fluorescence is activated by a UV light. This was taken about 1 km into a muddy passageway through rappels and squeezes. Different impurities cause different fluorescence colours. This is the only section of cave formations I have found that fluoresce such white and blue colours.

The photo was a long exposure with UV light painted on the formations.