Cave

Easier - A cave is a large hole. It may be underground, in the side of a hill or mountain, or under a cliff. A cavern is a large cave.

Caves are natural shelters. Animals often live in caves. A person who lives in a cave is called a cave dweller. During prehistoric times, cave dwellers painted pictures on the cave walls...

Harder - A cave is an underground hollow or passage that is formed when water runs through an area with enough force to dissolve or wear away rock. Over many years as the water evaporates and simply drips, it leaves tiny deposits of calcium carbonate (calcite). These drops form rock sculptures that look like icicles called stalactites and stalagmites. Stalactites hang from the ceiling and stalagmites form from the ground up. To remember the difference, stalactites have a 'c' in the word for 'ceiling' and stalagmites have a 'g' for 'ground.' If they come together in the center, they become columns.