What exactly is a cavern? Simple: it’s a hollow in a hill or mountain. This cavity is created by a collapse, meaning it’s not a cave. Caves are made by rivers. In the past, caverns were more important than you might think. Our prehistoric ancestors found them much nicer to live in than damp caves. The Cavern is also a surah from the Koran, which tells a story about how several men slept for years in a cavern. It turns out a cavern can be quite comfortable!