A cavern is a large cave, often with high ceilings and wide chambers that make you feel tiny when you stand inside. While a small cave might be just a hollow space in a hillside, a cavern is big enough to contain entire rooms, sometimes as large as a school gymnasium or even bigger.

Many caverns form over millions of years as underground water slowly dissolves limestone rock, creating enormous hollow spaces beneath the earth's surface. Inside, you might find stunning rock formations called stalactites hanging from the ceiling like stone icicles, and stalagmites growing up from the floor where mineral-rich water drips and deposits layers of rock over thousands of years.

Some famous caverns, like Mammoth Cave in Kentucky or Carlsbad Caverns in New Mexico, contain miles of underground passages that explorers can walk through. Without flashlights, these caverns sit in complete darkness because no sunlight reaches so far underground. The word suggests something grand and mysterious, which is why authors might describe a villain's hideout as a cavernous lair, or describe cavernous spaces that feel vast and echoey, like an empty warehouse.