If something reminds you of a cave or cavern in size, shape, or feel, you can describe it with the adjective cavernous. Your cavernous basement is huge, damp, and dark, but fortunately there are no bats down there.
Cavernous, "cavern," and "cave" all come from the same Latin root word cavus, meaning hollow. Anything that's vast or deep can be described as cavernous, like your favorite professor's cavernous knowledge about the subject of 17th century literature. As a medical or anatomical term, cavernous refers to something that is porous, particularly when it's filled with tiny blood vessels.