Waitomo Glowworm Cave (New Zealand)
The glowworms that give the Waitomo Caves their celestial ceilings use their bioluminescence to lure flying insects into sticky, beaded strands of mucous. More relevant to humans, they look really cool. So does the 52-foot waterfall that still flows during heavy rain. Tours are available, though the number of visitors allowed in is dependent on air quality, temperature, and humidity readings taken with the glowworms' health in mind.