You might expect lighting caves to be expensive but there are a few that do it themselves, and for free! “Glow-worm caves”, such as Waitomo in New Zealand, are lit up beautifully by the glow-worms clinging to their ceilings. The shine is taken off somewhat (no pun intended) when you find out the light really comes from worm snot. Hope they don’t sneeze…

More information:

scientificamerican.com/the-glowing-spider-worms-of-new-zealand/