The term LARGE CAVE can be summarized as a CAVERN, which is a six-letter word. A CAVERN is a large, naturally occurring underground space, often with a large opening to the surface and sometimes with spectacular formations of stalactites and stalagmites. Caverns are formed by the dissolution of soluble rocks such as limestone, dolomite, and gypsum. They can also form from the erosion of sandstone and other rocks.