Underground Worlds

Waitomo Glowworm Caves
(New Zealand)

Step into most caves, and you’ll be surrounded by darkness. But not in the Waitomo Glowworm Caves! There the walls are covered with twinkling lights. The light comes from glowworms. These are larvae, or immature forms, of insects called fungus gnats. They glow to attract insects to eat.

The caves are made of limestone, a type of sedimentary rock that dissolves in water. The rock was once on the ocean floor. Millions of years ago, the area rose above sea level. Rain created spaces in the rock, which grew to form underground caves.

You can tour the caves on foot or by boat, but don’t touch the walls! Glowworms make strings of sticky mucus to catch their buggy feasts.

Son Doong Cave
(Vietnam)

The Son Doong Cave is the largest known cave in the world. It’s so big, an entire New York City block could fit inside, including its skyscrapers!

The cave formed over millions of years as rivers dissolved spaces in limestone. Parts of the ceiling have collapsed, leaving holes that let in sunlight and rain. That has allowed a forest to grow on the cave floor.

The cave is also home to the tallest stalagmites ever discovered. These tower-like structures form when mineral-rich water drips from the cave ceiling. The water evaporates, leaving behind stacks of minerals. In the Son Doong Cave, some stalagmites are
24 stories tall!